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Ivan
Ivan, ASE Certified Master Technician
Category: GM
Satisfied Customers: 4871
Experience:  ASE Master Tech.20+ years exp. 9 years self employed. Participant on AutoLab Radio broadcast
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1997 GMC Yukon: wiring schematic..dome / courtesy light circuit

Resolved Question:

I need a complete and correct wiring schematic for the dome / courtesy light circuit in a 1997 GMC Yukon.
Submitted: 2 years ago.
Category: GM
Expert:  Ivan replied 2 years ago.

Hello and good morning. Here are your diagrams.

 

Your JA Expert,

Ivan

 

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Customer: replied 2 years ago.
Good morning Ivan, I think that may help but want to give you more info about the concise diagram I was hoping to get. This vehicle is an "SLE" and does have the keyless entry. While I do see the notes relative to w/ vs w/o keyless, I am wanting to make certain there are no conflicting details when it comes to the exact color coding. The dome lights are stuck on in this vehicle and I had pretty much narrowed down the problem to the interior lamp control module (which has all the entry exit fade stuff in it) but the local dealership suggests that vehicle (by vin#) does not have that module. They are saying those dome light features are controlled through the keyless entry module (receiver) instead. Other modules in that year supposedly count on the body control module for some of those functions. If you feel confident that those 3 pages are correct, the one additional diagram I will need would be the one showing the keyless entry receiver module with the dome light pin-outs shown as well.
Expert:  Ivan replied 2 years ago.

I feel confident enough, in that if your vehicle came into my shop, I would start with these diagrams. I recommend you begin with these 3 diagrams and come back to me if you find any conflicts. If you do, I will dig for additional info for you. Start with these and see if the colors pan out. They should. If you find some additional control wires or conflicts when you get to the interior lamp control module, I will pull up some body control diagrams, but let's go there only if warranted. Start your diagnostics with these and post back to me your findings and if you need more info. I'll be available to you if that comes to be the case.

Customer: replied 2 years ago.
Thanks Ivan, I am fairly convinced that I need to order that keyless entry receiver module. Even though the keyless entry does work properly, it appears there's enough going on in that module to be the cause of the dome lights staying on. There is no history of collision on the vehicle or signs of hacking to suggest there could be a pinched wire somewhere hence adding a ground condition to the dome light swiching circuit but I believe that in order to check the door switch wiring a bit further .... I am going to need to disconnect the keyless entry receiver. Can you suggest where I can find that so I can get it disconnected? Thanks ! Charlie
Expert:  Ivan replied 2 years ago.

You will find it under the left side of the dash. Below is a picture and I am providing the 2 diagrams for the keyless entry system too.

 

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Ivan, ASE Certified Master Technician
Category: GM
Satisfied Customers: 4871
Experience: ASE Master Tech.20+ years exp. 9 years self employed. Participant on AutoLab Radio broadcast
Ivan and 9 other GM Specialists are ready to help you
Customer: replied 2 years ago.
Ivan, there is a problem with the image you shared relative to the location of the door lock remote control receiver. There is a module near the location shown in the image but, it's not for the door locks. Disconnecting it did not disable the locks. Slightly to the right of that location, there is another module that appears to be a large heat sink and that heads upwards toward the firewall. Above thatyet and a bit futher to the right (about under the heater controls) is a blue plastic module but it's really hard to get at the connector and I didn't want to go further until I checked to see if you might have a different location listed or illustrated.
Expert:  Ivan replied 2 years ago.
Ok, I'm going to check.
Expert:  Ivan replied 2 years ago.

Take a look a these pictures and let me know what you think when you compare them to yours.

 

Manufacturer supplied 2 different possible locations.
Look for 5 wire connector with wire colors: gray, white, orange, pink & black.

#PIT3819: Location of Interior Lamp Control Module - keywords control dim dome electrical entry ground illumination inoperative keyless lens light remort resistor RKE short - (Dec 23, 2005)

Subject: Location of Interior Lamp Control Module.

Models: 1995-2000 Chevrolet C/K Trucks, Suburban and Tahoe 1995-2000 GMC Yukon and C/K Trucks Classic Body Style Only


The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this P1.

Condition/Concern

When diagnosing a dome lamp concern on one of the vehicles listed above, you may be unable to locate the

Interior Lamp Control Module that is called out in the Service Manual.

Recommendation/lnstructions :

Only vehicles without Remote Keyless Entry (RPO AUO) will be equipped with a Interior Lamp Control Module. If the vehicle is equipped with (RKE) Remote Keyless Entry, the illumination module is a internal part of RKE Module.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

 

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Customer: replied 2 years ago.
Those diagrams make things even more confusing because the text says that only vehicles "without" remote control receiver will have a interior lamp control module yet the illustrations show both modules in each example. Neither of those 2 illustrations depict what I have.
Expert:  Ivan replied 2 years ago.
Ok, I will look further. What is the production date of your truck? There may be a production cut that makes what you have a year newer or later.
Expert:  Ivan replied 2 years ago.

Take a look at this trouble chart and let me know where it leads you.

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Customer: replied 2 years ago.
Ivan, I can give you the vin # XXXXX that will help. I am uncertain of the production date. As far as the troubleshooting chart goes, I had already done the first 3 tests but can't do the 4th without knowing which module I have or where it really is.
Customer: replied 2 years ago.
The body style of this truck is still the version before GM rounded off the front lighting in 1998. My guess is that it really is a 1997.
Expert:  Ivan replied 2 years ago.

I have a good idea on how to narrow this down. You have a RPO list sticker in the truck, usually in the glove box. This is a sticker that has all the 3 digit option codes for the entire truck. Take a digital picture of it and upload it. I'll decipher the options and see what system is supposed to be in it. The sticker resembles this

 

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Customer: replied 2 years ago.

I hope it came out ok and I realy appreciate the help. I'm sure if I can get to the right module controlling the dome lights, I'll be able to go further with the troubleshooting and order a replacement.

 

 

Expert:  Ivan replied 2 years ago.
I dont see the image. Try it again and you use the paper clip in the task bar to import the picture. I'm running to pick up my kids and I'll decode everything as soon as I get back.
Customer: replied 2 years ago.
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Customer: replied 2 years ago.
Good morning Ivan, I think the upload went ok. Last night I did go ahead and revisit under the dash. The module that is the closest to where that first diagram indicated has a smaller connector with all smaller wires. It's rather long and heads upward. I disconnected it and the dome lights still came on when I reinstalled the fuse. The door locks also still worked remotely. The next module to the right has the appearance of a heat sink. The connector to that one is on the top of it and the module will need to be removed to access the connector. The next module to the right is way up but appears to have the larger style connector. All modules I speak of are located to the right of the steering column.
Expert:  Ivan replied 2 years ago.
Yes indeed, the picture came out great. I will decipher everything. If you can give me wire colors and wire counts and I will match them up to diagrams to identify what those modules are.
Customer: replied 2 years ago.
Ivan, After work today I stopped in at the local GM Dealership and talked to them about helping me to locate that module. All of their data showed it in the same location as your diagrams. While there's no details to support it, one tech suggested that the dome light and remote receiver stuff may be located in the body control module but that's a long shot especially since all of the wiring diagrams seem to concur when it comes to the remote lock receiver having the dome control stuff in it. They had no other suggestions for locating that module other than to bring the vehicle in and I am not about to do that at the risk of facing over 90 bucks an hour. I'll throw a toggle switch in and just interupt that dome circuit fuse before I will chance garage rates. For now, I am going to continue to look for that receiver module because all images I have seen for that look the same. It sure can't be too far away. I have identified the other modules that I have been able to see and none are the one we are looking for. I will hopefully find it this evening and keep you posted. Charlie
Expert:  Ivan replied 2 years ago.
Charlie, don't get discouraged yet. I'm going to decipher what you sent me after dinner and I would like you in the meantime to give me a list of wire colors for each of those modules in that area. I am going to match them to wiring diagrams and identify what they are. I promise, you will get some info from me this evening.

Ivan
Customer: replied 2 years ago.

Ivan, I believe I found it. I did find the primary door lock control module in the area from the illustration. It was up a bit higher. I disconnected it and when I hit the door lock button, I still heard a relay clicking. I stuffed my hand way up in above the steering column and felt another module. I felt a relay click coming from inside of it as well when I triggered the lock button. You can barely see the plug end from below but I got a mirror stuffed in and the plug looks like it's the one in the images and so does the size of the module. It's going to take me a good while this evening to get that out of there and down to where I can address the connector and disconnect it to further troubleshoot. You don't need to dig into those codes further for now. I will let you know how it goes in a couple hours. Charlie

Expert:  Ivan replied 2 years ago.
Great, engineers are not always our friend. Let me know how you make out or what you need from me later. I'll be here for you.
Customer: replied 2 years ago.

Thanks Ivan, for darned sure it'snot going to be real easy to get that module out. Looks like I will need to remove 2, 5/8" bolts and a 9/32" hex screw to loosen the plate that it's mounted to first and then go from there. That's why I elected to take a break for a bit. I am certain that clipping wire 156 will shut the lights off but I need to look a bit closer to decide whether that means the module is actually back because it looks like there are other connections to that module that could hold a fault too. I did electronics troubleshooting in servicing everything from CB's to Televisions for over 30 years and am still also a master electrician but mostly retired. Being analytical to that extent can sometimes be a curse ! I am no newcomer relative to zeroing in on the "what if's" then the "go to's". Overall that dome / coutesy circuit is a cake walk but when you throw in a module or 2, anything goes. Later !

Expert:  Ivan replied 2 years ago.

Once you understand electricity, you can figure out anything. Let me know if you need anything, I'm here for you,

 

Customer: replied 2 years ago.
Ivan, this is nuts..... I got the module lowered down enough to unplug the connector. Guess what? The lights still come on when I plug the fuse in. Actually, this might be a good thing because the cable with the receiver connector is so short coming from above that there's really no way to snip and reconnect wires for more troubleshooting. I'm taking a few minutes to more closely examine the diagrams and perhaps figure out where the mostly likely spot would be to look for the next possible fault which is beginning to look like a short to ground on the part of one of the door switch wires. It seems apparant that the module does not supply the 12 volts for the dome circuit and that supply is definitely active to the lights so..... it's got to be a problem in the control link which is ground switched for the most part. But....... I am also thinking that it might be possible that the door lock receiver module may be responsible for shunting the dome lights out of the "on" mode hence, unplugging it would not "prove" the module is ok. Your thoughts when you can? I'll be out in the garage a bit again.
Customer: replied 2 years ago.
New details .... I studied the diagrams further yet and if they are correct, the dome light override totally disconnects all of the door switches so that rules out a short to ground in the wiring of those. This now brings me back to the module.... from what I see, there are only 2 connections to that as far as the dome light circuit goes. One goes to the dome override switch and the other goes to the dome light +12 volts which we know is active. I did open the module and see 3 relays. My guess is that 2 are for the lock commands (lock & unlock) and the other is for the dome lights. Since the module's function is apparantly not to interupt the dome light circuit (as evidenced by the fact that removing it does not kill the dome lights) it somehow needs to shunt that circuit (rather than disconnect it) and even there, I have a problem in thinking that because then there would need to be a giant resistor and heat sink to make that happen especially since there's a "fade" feature in the picture. I suppose that from here, some expertise on how that module factors into the dome light scenario is needed. What it does for the door locks is very clear but what it actually does for the dome circuit is not at all clear. I'm really about done with this for the day so don't make yourself nuts tonight. I am hoping you may have access to more logic on that module's roll or something rings a bell from your experiences. Many thanks ! Charlie
Expert:  Ivan replied 2 years ago.

I'm supplying you the description and operation of the dome light circuit. I figure this will help you interpret what you have to this point, I'll put my thoughts at the end of this.

 

Voltage is supplied at all times from the CTSY Fuse 3 to the Courtesy Lamps, Dome Lamps and I/P Compartment Box Lamp. The Courtesy and Dome Lamps turn on when a ground path is provided by the Headlamp and Panel Dimmer Switch or one of the Door Jamb Switches.

The I/P Compartment Box and Vanity Lamps have their own Switches that provide ground paths when their Switches close.

UNDERHOOD REEL LAMP
Voltage is supplied at all times to the Underhood Reel Lamp from the Horn Minifuse. When the Switch is closed a ground path is provided.

COMPONENT ILLUMINATION LAMPS
When the Headlamp and Panel Dimmer Switch is turned to the PARK or HEAD position, voltage is applied through the PARK LPS FUSE 9 and the closed contacts of the Headlamp and Panel Dimmer Switch to the Component Illumination Lamps. Since all of the Component Illumination Lamps are grounded G200, they light.

ILLUMINATED ENTRY
When a door is opened, the Illuminated Entry System is activated. After the last door is closed, the Dome Lamps will remain illuminated for 20 seconds or until the Ignition Switch is turned on which cancels this function. Voltage is supplied to the Module at all times through CTSY Fuse 3. The ground path is provided by CKT 150 to Ground G200. The Module senses a ground signal from CKT 157 when a door is opened. The Module then provides a ground path to CKT 156 which allows the Lamps to illuminate.

 

 

Control is definitely on the ground circuit side. That means that by unplugging, the lights can default to on. Grounding my be present to defeat the circuit at the module. Many times that causes the system to default on. Let me know your thoughts as you read this.
Customer: replied 2 years ago.
Ivan.... those details will be helpful for me to consider when I get back to the project later today. As I read them and began to feel more confident in thinking the module could be the culprit, something still didn't connect. If the absolute only switching is "ground path" for that circuit, then the only source of the ground would HAVE to be through that module. Think about this, that module supposedly is the only item that can override all other switches in order to perform the 20 second delay. Although the dome override switch disables all dome lights, it does not do that when the illuminated entry feature is activated by the module so there again, the module would have to be providing that ground path through itself. That is now taking me back to "how can those lights be on with the module disconnected?". If the module is responsible for supplying the ground, it just can't do that when disconnected. If it's not solely responsible for providing the ground, then I can't see how it can interupt a ground that's supplied else where. You can't eliminate a ground by supplying a second ground. If the module's function was to "add" a ground to "kill" the lights, that would be different. This is why I was really surprised that the removal of that module did not kill the lights. If you gain more thoughts on this today, I would appreciate you sharing them. I will be back at the project later today but not yet sure where my next direction needs to be. Charlie
Expert:  Ivan replied 2 years ago.
I think you are thinking correctly. Headlight systems on many cars, are controlled the same way, so when you disconnect the headlight switch, the headlights come on because the ground path has been removed. If you open the cover, you can trace the board and see where ground is present or isn't present. From there you can determine if the issue is coming from outside or inside that module. It is most likely the module that is causing the issues.
Customer: replied 2 years ago.
Ivan, if you have a solid contact.... the key question that remains is; In a vehicle like this with a fully functional dome light circuit, would the removal of the module cause the dome lights to come on and stay on? If that's the case, I am pretty sure I need to get a module. If the removal of the module causes the dome lights NOT to work, I need to do more circuit troubleshooting. Troubleshooting the module itself will be out of the question without a schematic of it and for certain that's not where I want to go.
Customer: replied 2 years ago.
New details .... I disconnected the Headlight, dome defeat, dimmer cluster and in taking readings at that plug, point "M", white wire #156 is shorted to ground. This is with the receiver module still out of circuit. I think I am onto something. I also check point "L", purple wire for the door switches and it reads open with all doors closed and then goes to ground when any door is opened. That confirms that the door switch wiring is ok. Now, to look further into where 156 is shorted to ground is going to be a task without some isolating. I see there are 3 junction points shown.... S209, S246 and S417. I also see there are at least 2 points with connectors.... C298 and C301. Do you have a location list for them? Also, in your experiences are there likely areas where a wire could become pinched to ground or may be routed near where a body screw that was removed and reinstalled could be causing the short? Thanks again .... Charlie
Expert:  Ivan replied 2 years ago.

Did you do that last step of that trouble chart, where it wants you to test cavity B of the lighting control module to ground with a volt meter. It says if you have a volt reading of less than 10 volts, the module is to blame. Cavity B is the gray wire. I know the diagram shows that gray wire going to the remote lock receiver, but see if you have a gray wire on yours. On all of the diagrams, the lighting control module is a magic white box, no details are given. Let me know if your module shows a gray wire on that terminal. It wants this test with the dome switches disconnected. What I recommend too, is if you have that remote lock receiver, take your reading, then disconnect it and see if the lights go out, with the door switches disconnected. Including the rear door switches. Check your voltage on that gray wire. If you disconnect that remote lock receiver and the lights go out, I feel that is the module to blame. On that module power comes in from the headlight on the gray wire and goes out on the white to the lights. See what you find there. Ok, i just read your updated info. Under the floor is the most common point for issues. Wetness is usually the reason. I'll be right back with locations for those points. Here is some info. Let me know if you need more. There are 3 pictures for C301, so take a look on yours.

 

 

S209:

I/P Harness, approx. 12 cm into Crossbody Harness Breakout, toward C298

S246: Crossbody Harness, approx. 41.5 cm from LH Door Harness Breakout, toward C301

 

S417: Front to rear Body Harness, approx. 230 cm into Crossbody

 

Customer: replied 2 years ago.

Ivan, here's what I did tonight since I found the short to ground on 156. While that still doesn't rule out module problems, that short can not be there no matter what. I took down both dome clusters from the ceiling to be sure no screws were through the wires. They are both ok for that. I also pulled both sun visors to inspect for the same. While doing this, I kept the dome light fuse in place in the event an intermittant would show up during the disturbances. Last, I pulled the side panel at the driver's side area where the hood release is to expose all of the connectors in that body well. I disconnected one at a time and the short remained and ... the dome lights stayed on except in the case of the white connector. Unplugging that shut the lights down totally. I ran out of time to put the headlight cluster switch back into place (since it has the dome override in it) to see what happens then with that white connector unplugged. Here's where I am at right now Ivan, I want to rule out a ground fault in each door (not dome light switch wiring. That's all ok) but because all 4 doors also have the side lights in them with a 156 line. After that, it can be under the dash or anywhere that 156 is routed. I'm going to print out those locations in the morning as well and see what that yields. I really appreciate all the details and we're going to solve this soon.

Expert:  Ivan replied 2 years ago.
I'm here with you until its fixed. Just let me know how you narrowed it to the 156 circuit, I want to be the backup to your thoughts and testing.
Customer: replied 2 years ago.
Ivan, with the dome light override, headlight, dash dimmer/courtesy on switch assembly unplugged and, the module unplgged... all door switches are removed from the equation and there are no other devices then in line to send 156 to ground that I can see in any diagram. (If you know of something else, feel free to let me know.) At that state, I read 156 at the headlight switch assembly plug and it's dead shorted to ground and that state does not change at all when fuse #3 is plugged in which confims the grouding of 156. I had some initial concerns about the reading being flawed due to the fact that many bulbs are in place which can throw resistance into the loop but I am sure that is not the case. If you come up with any more thoughts relative to where a likely place is for a short in 156, let me know. I will be resuming the search later today.
Expert:  Ivan replied 2 years ago.
156 goes into the remote lock receiver too, so disconnect that one too. If your truck has factory keyless entry, it appears the gray wire from the headlight switch goes to the receiver instead of the lighting control module and control over the white wire comes from there instead of the module. Ive been relooking at the diagrams again.
Expert:  Ivan replied 2 years ago.
Actually I will ammend that a bit. If the headlamp switch is unplugged, that is where 157 and 156 meet, so if you are grounded on 156 with all of those items unplugged, I'm in agreement with you.
Customer: replied 2 years ago.
I am going to get back to the project in a couple hours but wanted to make a note... I see what's going now with the receiver module's function relative to the dome light circuit. Even though I need to find that short, I had a need to get personal with that module. 157 goes to it so the module can give 156 the ground it needs even when the dome override switch is depressed. For it's main function, it takes 156 to ground to assume the grounding role that 328 (door switches) normally takes. In all of those cases, the ground that goes to the module is the ground that is used for all dome functions controlled by the module. In the normal dome light mode, the grounds are provided by the actual door switch grounds. I'll be willing to bet that if I can find this ground short in 156, the module will prove out to be fine. Any more hints on a likely place for this ground short to be ?
Expert:  Ivan replied 2 years ago.
Here is what I recommend. Find major branches for 156. Find an easy to repair section and cut the wire isolating one section from another. See which side still is shorted to ground, then work your way orderly through the system that way. I am betting it is under your carpet.
Customer: replied 2 years ago.

Ivan, I am about to go back at it. Note, this vehicle is pristine. Can't find a spec of rust anywhere. TThe steel under some of the carpet I lifted when I bought the vehicle is showroom so even though I am not ruling out the fault being under the carpet somewhere, I doubt it will be because of moisture. Since there are no wiring faults of any other nature, I think that the cause of this fault is because of something having been taken apart and then during reassembly, a screw went through a wire. I would generally more so considerwire rotting from moisture in the case where there is an "open" circuit.

Now, relative to the carpeting and dome light wiring underneath it..... would that wiring be under the floor board panels at each of the doors or does some run up the middle as well? I'll check back in a bit. Heading out to work with C301.

Expert:  Ivan replied 2 years ago.
What I have found in the past is dry carpeting with a wet area under the insulation, then green wiring from corrosion. If you find some solid areas to cut, soldering them back together again after of course, set your meter to check short to ground, cut a section and see if the ground lifts, then you know it is beyond your cut. Do this systematically, reconnect the meter to your cut section and do it again. You will be able to narrow it down that way.
Customer: replied 2 years ago.

More hints.... I disconnected C301 which does shut the lights off. After plugging in the headlamp switch assembly, I was able to use the courtesy switch to turn the door lights on but that did not turn on the dome lights on so there's a chance that C301 does interupt the fault but.... with C301 disconnected, I still read a short to ground on the white wire (156) at both the make and female sides.

 

Now, I went to the passenger side and pulled the lower kick cover. I disconnected all 3 connectors there and the lights still stayed on. Does that rule out the ground fault being on the passenger side ?

 

Last question for now .... Do you have access to any other kind of map that would more clearlty show all of the routing of wire 156 ? I know it is present in each of the 4 doors because of the marker lights. I also know it's under the dash and .... overhead to run the 2 sets of dome lights but just not sure how 156 gets there. I'm going back at it for a while. PS... In my earlier exploring, there's not a spec of corrosion at any connectors and as much of any harnessed that I exposed, the wiring is super clean.

Expert:  Ivan replied 2 years ago.

I would agree, that the issue is upstream from that passenger side. I don't have a harness routing picture. I do have a factory wiring diagram, which may be what you are looking at as well. With the connector references, I can get illustrations and locations that can help form the picture of the routing. I do believe, if you have the bulbs in place, you may still show a ground as well. To truly test for continuity to ground, every item needs to be disconnected from the circuit and the fuse removed so the circuit is unpowered. Then you can go section by section, checking for continuity to ground.

Customer: replied 2 years ago.

Good morning, I think my next step is going to be to actually cut the white wire at C301 so that way the other conductors at that connector will remain in place. As far as pulling out all the bulbs go, according to the diagrams I have... pulling the fuse lifts that side of the circuit from everything. I'm using both an analog meter and... a digital to make certain I see 0 ohms to ground on 156 confirming a total short. I wish that the junctions for 156 were easier to locate and access because that would make it easier to separate them and narrow things down tighter.

 

Do you know if there are more factory connectors in the door posts between the front and rear doors? That might get me closer to ruling out a problem in the doors themselves. I am headed in that direction because of the likelyhood that something in a door may have needed to be repaired at some point in time and 156 is definitely in each door. Also, to learn where the wiring is routed to get to the dome lights will be helpful.
Actually, any hints you can find about the 156 wiring will be helpful. Just finding and cutting every white wire may be the wrong approach until I exhaust other search means first.

 

I won't be back at this until later today so feel free to share more. Thanks again, Charlie

 

 

Expert:  Ivan replied 2 years ago.

See if you can match up the splice locations that I gave earlier. I would definitely work systematically to eliminate big sections of 156 as you can. I think the splices are under the carpet, see if you can verify where the harnesses cross the body.

Expert:  Ivan replied 2 years ago.

The only other connectors are C298 and C302. C302 is next to C301. C298 is in the dash as indicated below,

graphic

Customer: replied 2 years ago.
Ivan, I am about to go back at it for a while soon. The reason I asked about any connectors for 156 at the bases of the door posts between the front and the rear is because the diagrams I have do not show the courtesy/marker lights in the doors. I'm thinking that if you had a diagram that also showed those in addition to the lights shown in the diagrams I already have, there might be notes about connectors other than C301, 302 and 398. It would be so much easier to make those disconnects than to actually be cutting the white wires at the door themselves.
Expert:  Ivan replied 2 years ago.
I will send you what I have. See if that has more detail.
Expert:  Ivan replied 2 years ago.

Here are my diagrams

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Customer: replied 2 years ago.

Ivan, new details. I think C301 is the key point from here. Tonight, I plugged the receiver module back in and also reconnected the headlight switch. With C301 disconnected, the system and door lights and under dash lights all work properly even with the delay feature going. The 2 dome lights do not work at all. There are actually 2 white wires in the C301 connection. My guess now is that the fault is somewhere between C301 and, the ceiling dome lights. Every thing else is pretty much ruled out. Last step I did for the evening, I cut one of those white wires and plugged C301 back in. The dome lights then came on but, they do not go off with the rest of them when the module times out. I did not yet print out the diagrams you shared a bit ago but with what you may be able to lend from here would be your though on how the wires get from C301 to the dome lights. Any hints will be helpful. I'm almost there and already glad I don't need to buy that module.

Expert:  Ivan replied 2 years ago.
Usually those wires, if in the center area of the headliner, travel straight up. Here is the location for C305 that goes to the front headliner (In Headliner at #1 Roof Bow). Here is S417 which splits to go to that connector

(2-Door Utility)
Front to rear Body Harness, approx. 34 cm from Front Dome Lamp Breakout, toward C301

C301 has the 156 feed to the dome lights, at S417, it splits to the front and rear dome lights. The harness usually goes straight to the side then down to the rail from the dome light. Whichever side is the C301 that affected the lights, that will be the side that the harness comes down on.
Customer: replied 2 years ago.
Ivan, this is a 4 door unit. Are you saying that C301 heads from the driver kick panel under the plastic rocker cover and to the door post then up?
Expert:  Ivan replied 2 years ago.
Yes, follow it up the rail and you should find the breakout the sends it up. It splits and travels to the rear dome light too.
Customer: replied 2 years ago.
Hi Ivan, I didn't have a lot of time for the project this evening but I was able to finally pull off the rail cover going up between the front and rear door. That took over an hour but only to show no wires going up toward the headliner. The factory bundle that has 156 in it slides back and forth real easy under the plastic channel cover at the front door and it's all looking clean. That bundle then goes across the rail at the floor and continues under the rear door floor channel. I'm thinking the the 156 line may head upwards at the pillar at the rear seat rear. I may drop the dome assemblies down again to see if the wires might yield more hints as to where they head down. I remain mostly convinced that this is the area for the fault and am going to follow this out further. Again, every thing works perfect now with the fuse in and that 1, 156 wire cut at C301 except that the 2 ceiling dome lights remain on as long as that fuse is in no matter what. What really sucks in this is that each side of that cut wire reads a short to ground when C301 is connected. With it disconnected, on one side reads a short to ground. I will have more time in the morning to continue. If you have any more input, feel free to share.
Expert:  Ivan replied 2 years ago.

Take the bulbs out of the dome light and see if you still have a short to ground on that wire.

Customer: replied 2 years ago.
Ivan, I just pulled both dome lights down and removed the bulbs. There is a short to ground on each which I pretty much expected since they remain on in all modes. Now it's still all about locating that short. With the dome lights now down, I am going to try to learn where the 156 line from each of them joins. It appears that could be about anywhere from the dome lights all the way to C301. Snipping that one white wire @ C301 and gaining full function of all of the other lights tells me that the short is going to be on the dome light side of where ever the other lights' 156 line and the dome lights' 156 line connect. Any more input will be appreciated.
Expert:  Ivan replied 2 years ago.
Yes, i am in agreement with your thoughts. Drop the dome lights housings and you should be able to see the direction of the harness.
Customer: replied 2 years ago.
Well Ivan, this is nuts. With the dome lights pulled down and bulbs out, I located the cable bundle going across the top of the rear, left door and pulled some slack to be able to work on it. One end heads to the rear toward the post behind the rear door. The other end heads forward and by pulling a bit, heads then over to the front dome carrying 2 orange wires, 2 black wires and one white wire. One orange and black is for the dome light and the other orange and black are probably for the courtesy lights at the front ceiling. I cut the white white there above the rear door and read 12 volts (probably because the other bulbs are still in place) on one side and nothing on the other. Hmmmmm. I did do a bit of tugging on the dome light wires and that bundle over the rear door but some thing then suggested that the fault may have been interupted in all of that so I put the fuse back in and guess what? All the lights work properly. I then reconnected that white 156 line that I had cut at C301 and it made no change. All is fine. Cripes.... I really hate when that happens because now I have no idea where that fault could have been but I do have a feeling that some where between the front/rear door post, the rear rear door post and the ceiling, 156 may have been pinched and it's now releaved. Over the last few days I've also talked to a number of GM techs to try to get an idea of where a fault like that is most likely to occur as a result of other repairs and most agreed that the doors would be the first place. Another also noted that the dome lights themselves could be the area because the bulbs for the courtesy lights are sometimes difficult to change and when they get reinstalled it's easy to pinch the ground under one of the 2 screws. I did rule that out way early on as I also ruled out the doors. At any rate, for the moment this is solved you have been very helpful. I would like to get some more money going your way for the help that was beyond what I agreed to pay. Can you tell me how to do that please? Additionally, you are going to get some amazing feedback. Many thanks again, Charlie
Expert:  Ivan replied 2 years ago.

Charlie, I know how you feel about issues that cure themselves. I see things the same way. Chances are one of the contacts from one of these lights were touching the body and you cured it by your wiggling and tugging. At least you know if it returns, it is above the headliner. If you press the button that allows you to pay for the answer, there will be an option to add a bonus. That will let you do what you wish. Also, if the problem ever returns, just ask for me, and I'll be happy to help you again. It was a pleasure working with you.

Ivan

Ivan, ASE Certified Master Technician
Category: GM
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