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Dave, Jeep Master Tech
Category: Jeep
Satisfied Customers: 1158
Experience:  Chrysler Triple Master, ASE master Tech AA degree in Auto.
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Rear window defrost doesnt work. Relay works because I can

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Rear window defrost doesn't work. Relay works because I can hear it clicking on and off. On switch lights up. Tabs are solid and don't see any breaks in the lines. Does this jeep (2001 jeep cherokee) have a seperate timer? Can the on/off switch be bad and still light up?

Hi, the switch can still be bad even if the light comes on and the rear defroster does have a timer.


However, what you are going to want to do is test for power and ground at the rear window. You will need either a test light or a volt/ohm meter.


With a test light put one end on one of the tabs and the other end on the other tab. Turn the rear defroster on and see if the light lights. If it does then the problem is in the window. Do the same thing with a volt meter and see if it registers any voltage.


Let me know what you get and we will go to the next step after that.



Customer: replied 7 years ago.
Don't get anything. Set the volt meter to 20V. One other thing I will need to check is the wires being connected at the entrance of the hatch. I had the hatch replaced and it's possible he didn't reconnect the wires. However, the defrost didn't work prior to having this done and it's the same window.

Ok, let me get you the schematic for the defroster, then we can talk on the same page and stat to work back to the problem.



Customer: replied 7 years ago.
sounds good. I took off the plastic and everything seems to be hooked up.

Ok, the next thing we need to do is to determine if it is power or ground that we have lost. With the volt/ohm meter set it to ohms, put the neg lead on a good ground (anything that would connect to the frame and the other end to eith of the tabs and see if you have anything, then do the same to the other tab. Let me know what you get.


Also here is the schematic





Customer: replied 7 years ago.

I used the leaf spring to ground. Used all ohm settings and it always read 1 ohm. Same thing on both tabs

Ok, that would tell me the ground side is good and the power side wiring is also grounded as it should be until you give it power.


Let me back up here a bit. When you checked for power was the key in the run position and the switch on? Also check it again with the key on and switch on with the ground lead on the leaf spring and the pos lead on each tab. Volt meter again set to 20 volts DC.


If you still have no voltage then what we need to do is pull the rear defogger relay. i know you said you hear it click but that doesn't mean the contacts are any good inside the relay. With the key off you should have power at terminal 30 and with the key in run you should have power at 30 and 86. Then with the switch turned on you should have a ground source at terminal 85.


Let me know



Customer: replied 7 years ago.
I'll check this out tomorrow and get back. I think at one point I pulled a relay out that I know worked and tried it in the defogger slot. It didn't do anything. I'll check this stuff out tomorrow and let you know what I get.

Sounds good, I will be in and out tomorrow but will keep checking for your info and then get back to you.


Then the relay is most likely good so by doing these tests we will find out which power is missing or if the switch isn't crating the ground we need.



Customer: replied 7 years ago.
I pulled the horn relay out which works and switched with defrost relay. horn still works after this. doesn't this mean relay is good? i can't view this online anymore, just my phone. can't pull up the schematic on phone. also, i did have power switch on during all testing. with switch on and 20V setting, no reading at terminal. can we jump switch? with 4 wires i'm not sure which ones to jump.
Customer: replied 7 years ago.
I unhooked the switch and have 4 wires. black, dark blue (white stripe) , light blue (yellow stripe), orange. dark blue has 13.3V ouyput. assume black ground, i used paper clip and jumped to other two wires (one at a time). still no volts at tabs. is this correct procedure? maybe i should run new test wire from switch to tabs and see if heat works?

Hi, as I mentioned in my earlier post one of the reasons to test the terminals at the relay socket not relay is to determine if we are loosing one of the powers or the ground. Yes I would agree that the relay itself is most likely good.


What you need to do is test for power at the relay socket, with the key in run and the defrost switch turned on you should get two terminals with battery voltage and one with a ground source. If you then turn the defrost switch off you will loose the ground source but both voltages should remain as long as the key is in run.


By doing this we will know which direction the problem is, either back to the defrost switch, back to the ignition switch or from the relay to the window.


Let me know what you find at the relay socket.



Customer: replied 7 years ago.
Power @ 30 with key off. power @ 30 & 86 with key on. turned on switch and pulled relay out, 85 doesn't show anything. should I be testing for volts on 85? I bought this jeep last year. it had a rigged power cable running from alternator thru steering column to power something. i removed it since it was live and unused. As far as ground, I get shocked every time i shut door. in winter it is bad. anyway, am i testing 85 correct?

Hi, 85 should be a ground that is created by turning the defrost switch on. So as long as you have your meter set to ohms and the neg lead to a known good ground and the other lead to the relay socket terminal you are testing it correctly and should show continuity if it is good.


If you do not get continuity take a jumper and put it from a good ground to the dark blue with white wire at pin 2 of the switch connector. Now test for ground at the relay terminal.


If you now have ground there the switch is bad. If you still do not have ground there then the wiring between the switch and the instrument cluster, the instrument cluster or the wiring from the instrument cluster to the relay socket is bad.


The instrument cluster senses what the switch is doing and then either completes the ground path to the relay or opens the path.

If you have ground there, put the relay back in and see if the defrosters work.



Edited by Dave on 9/28/2009 at 4:07 PM EST
Customer: replied 7 years ago.
turned on jeep. turned on switch, removed relay, paper clip in slot two connected to good ground, red lead connected to 85 and black lead to good ground. ohms always read 1. usually it goes to 0.00 when i'm touching good ground.

Hi, Sorry if I caused a little confusion here. What you need to do is to have key in run, defroster on, relay removed, check for ground at relay socket terminal 85. So have your meter on ohms, red lead on terminal 85 and black lead of battery ground post. You should have a ground signal or show some ohms.


Let me know.



Customer: replied 7 years ago.

I think that's what I did. Except I used the door hinge as a ground. It worked as a ground when I was testing voltage for 30 and 86. My ohm meter always reads 1 and then goes to 0 when I get continuity. I didn't get anything. I will do this again and check 85 with a jumper connected to the battery as a ground. It won't be until this evening when I get home. I will also try to test the tabs again with this same ground. I'm second guessing the leaf spring as a good ground in the previous tests. I'll give you all this info later. Thanks

Sounds good, I will be gone until about 8pm central but will get back to you as soon as I can after that.



Customer: replied 7 years ago.

Ok Dave,


I tried to redo things for you. Things don't seem different but I'll let you decide. I'll try to keep it condensed. I used a jumper cable with a 19 gauge wire extension for all the grounding directly to the battery. First I turned key and switch on while relay was installed. blk to ground, red to tab gives .21ohms on each tab and 0.0volts on each tab. blk to one tab and red to other gives 0.00 ohms and volts. Next, with switch on and relay out it gives 13.5V to 30 and 86. It gives .02V and 1.0 ohms to 85. Isn't that showing no continuity when it stays at 1? Next I turned on switch with power and relay installed and touched the 19 ga grd wire to the blue/white wire on the switch. It would turn the switch on/off each time I touched and removed this jump wire. I measured the volts between the tabs and it was still 0.00volts. Last I took the relay out and measured 85 at .02 ohm and 0.00 volts. At this point I had pretty much confused myself. Would it help to run that 19 ga wire from the switch directly to the tabs to rule out the wiring from switch to tabs? Or have you already ruled this out? Get back when you get a chance. I'll be around all night if I need to try something else. Thanks!

Hi, when you tested the ground at term 85 at it showed 1 ohm that is a good ground with good continuity. If the display on the meter didn't change after placing the leads on the terminal and ground then it would be open, no continuity. If it were to display high ohms then it is a bad ground.


So at this point it appears we have both powers and a good ground at the relay. The last test to verify the ckts to the relay is to repeat the one for testing ground at terminal 85=key on, switch on, relay out, meter on ohms, neg lead to ground pos lead to terminal. Note meter reading, now turn the switch off, leave everything else the same just turn the switch off and record the meter reading. I want to make sure we see a change.


The reason the light goes on and off when you touch the ground wire to the blue/white wire is because you are giving the voltage a easier path to ground so no power is going to the light on the switch. Becareful doing this has you can blow fuses and even computers by putting a ground to a power source without a load in-between.


If everything checks out good on this next test then it is time to work towards the window checking for voltage and ground at the variouse connectors. While you run this test I will get the infor as what connectors to test and where they are located.



Also , do you have heated outsedie mirrors? If so, do they warm up if you turn the rear defrosters on? This will tell us if any part of the ckt is working.
Customer: replied 7 years ago.
No heated mirrors. Dave, when I turn on my ohm meter it reads 1 by default. It seems that when I complete a circuit it goes to 0. I will do the test but I'm going to guess the ohms will read one and will never change. I'll get back in a few minutes.
Customer: replied 7 years ago.
Reads one all the time. Never changed. On the ohm meter I have, if I touch the black and red leads it goes from 1 to 0. Isn't that the same as have continuity? So wouldn't 0 be good on the readings I'm getting and 1 would be no continuity?

Yes, you are right on your meter 1 is a open. I took it has 1 ohm which is a good ground.


Alright then we know the problem, you are not getting the ground signal from the switch to the relay.


With the key in run relay out, put a jumper between terminals 87 and 30 and see if the rear defrosters now have power between the tabs. Set meter to 20VDC put one lead on one tab and the other lead on the other tab.



Customer: replied 7 years ago.

0 volts between tabs unfortunatelly.

Alright, do the same thing but put the neg lead to the battery ground and check both tabs for voltage.


I hate to think we have two problems with the rear defrosters.


The first way I had you check for voltage may actually be correct if all the voltage is being used up between the grid.

Customer: replied 7 years ago.
0 volts on each.

Well something is not making any sense. If you have battery voltage at terminal 30 of the relay socket and you have a jumper from that terminal to terminal 87 of the relay socket then you should have voltage at the black and white wire at the rear defogger.


If you do not then there has to be a brake in the black with white wire someplace between the relay socket and the rear defogger tab.


There are three connectors this wire goes threw. they are connector 326 pin 4, c312 pin 2 and c310 pin 3.


c326 is located behind the left rear quarter panel and c312 and c310 are located top center of liftgate.


c326 is a black connector, c312 is green and c310 is black.


Check for voltage at c326 first. seperate the connector and test at the specified pin. If you have voltage there then move onto the next connector then the next until you find out where the voltage is lost at.


If there is no voltage at c326 pin 4 then there is a brake in the wire between that connector at the relay socket. If voltage is lost between connectors then the wire is busted between those connectors. Where ever it is a new wire will need to be installed.


let me know


Here are a couple figures showing where the connectors are located.





Customer: replied 7 years ago.
will do that tomorrow and let you know what i find out. thanks dave

Sounds good, sorry it seems to be taking so long. Sometimes these electrical problems are hard to track down but I will continue to help you till we get to the bottom of it



Customer: replied 7 years ago.
No problem. I know, it's like working on a computer. why do you think i'm getting after this now before we've even had our first frost. i knew it could take some time.
Customer: replied 7 years ago.
Ok, have disassembled back end. Mine looks a little different than pic you gave. I have 4 white connectors and one doesn't have anything attaching to it. One has a large black/white stripe wire with 4 other wires as well. Another has a large black wire with a bunch of other wires. Here's a pic of the one I think it is. Does the connector I'm looking for have a total of 5 pins? This one has power at the black/white stripe wire. When I get to the top of the tailgate I don't have power to the black/white stripe wire on the green connector. Am I testing the correct wire and can I jump this wire to see if the problem is this wire going up to the tailgate?
Customer: replied 7 years ago.
Customer: replied 7 years ago.



I found the problem. The black/white wire was pinched in half where it exits the body and enters the hatch. Is it safe to crimp a spliced wire and bypass the green connector so I don't have to mess with it? The break is very close to the green connector and doesn't really give me room to splice back together. What guage wire do I need to get?

Hi, sorry it took so long to get back to you today, i was out most the day on other issues.


Glad to hear you found the problem. Yes it is fine to bypass the connector and splice the wire together. Use 20 gauge wire for the splice.


Is there anything else i can do for you? Id not please choose accept so i can get paid.


And good work doing the tests and following the problem through the ckt.



Edited by Dave on 9/29/2009 at 8:47 PM EST
Dave and 3 other Jeep Specialists are ready to help you
Customer: replied 7 years ago.

I might have some more for you to help with. I'll accept so you get paid for this one but how do I get you back for more help? My front speakers don't work and I get severly shocked every time I touch the door when shutting it. I know the speakers work because I swapped one with the back and it worked there. Also, I ordered a duplicated factory radio thinking it might be the unit but the same problem exists. I'm wondering if it's a similar problem as the window defogger. Anyway, I want to get the defogger working first and then move to that stuff. It would be great if I could get your help but I don't know if I can get you back.

Hi, I am not sure how you would do that either except to address the question to me by name.


Thanks for the accept and bonus i really do appreciate it.



Customer: replied 7 years ago.



I now have 12v across the tabs and the window heats up. Thanks again. Hope to work with you again on other issues.

Congrats pal, good job. Hope i can help you again when you need it. You were great to work with.