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Gary, GM Technician
Category: GMC
Satisfied Customers: 1057
Experience:  Senior Technician
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GMC Sierra 1500: Trailer brake lights and and cruise control

Customer Question

Trailer brake lights and and cruise control not working.
Submitted: 2 years ago.
Category: GMC
Expert:  Chris (aka-Moose) replied 2 years ago.
I am sorry for the delay in getting a response to you. Sometimes we get alot of customers and just can not keep up. Sometimes you just have to wait for the correct tech to login.Do you even still need help. Sometimes customers seek help elsewhere or figure it out on their own before we get to each and everyone.I am sure I can help a lot or a little at least something if you give me a chance and work with me. I am going to get an answer to you regardless if you reply or not sooner or later.If your concern is urgent reply and let me know and if you have anything more you think will help me, to help you, let me know. I work on here normally 3pm-3am central. Thanks Chris
Expert:  Chris (aka-Moose) replied 2 years ago.
Are all trailer brake lights not operating? If so can you do electrical testing and read wire diagrams?Does the horn work, and are there concerns with the air bag light? You want a excellent 5 star answer & I would like to be rated the same for providing it. Consider I don't know your skill level & I can't see, smell, hear, or touch the vehicle. It may take a few back and forth replies. Try your best to respond with good detail so I can do the same. I normally log in at 3pm and work late. A rating is required. Your rating me, what I type. I am not an employee of this website, nor have control over the fees or the time it took to get a response. If you rate negative or not at all you still paid, but I get nothing. I want you pleased with me and my efforts, so let me know if your experience here has come up short.Thanks Chris
Customer: replied 2 years ago.

Both left and right trailer lights not working but both turn signals work. The trailer bulbs of course are single filament. Cruise control not working either. I'm told that this usually occurs together. Truck brake lights were working at the time of my original question but now they do not work either. I haven't checked the light bulbs on the truck yet but I will do that now.

Expert:  Chris (aka-Moose) replied 2 years ago.
On the truck the brake lights, all 3 do not work?On the truck the rear turn signals do work?On the trailer the turn signals work?On the trailer the brake lights do not work?Did I understand that correct?
Customer: replied 2 years ago.

Yes, except that the left and right brake lights do not work and the center light works.

Expert:  Chris (aka-Moose) replied 2 years ago.
These are signs that the multifunction turn signal switch is faulty. Would you like the wire diagrams to test it?
Customer: replied 2 years ago.
Yes , please.
Customer: replied 2 years ago.
It's taking a long time to get a response.
Expert:  Chris (aka-Moose) replied 2 years ago.
The hours you and I work are not the same. Open the link below.
Customer: replied 2 years ago.

I have studied these diagrams as well as the ones in my repair book and don't know how to proceed. Too many "black boxes" and I don't know what is going on inside them..

What's next?

Customer: replied 2 years ago.
It seems that you have limited time to help me. I need to fix this problem as soon as possible for obvious safety reasons. A once a day response is not likely to solve the problem in a reasonable amount of time.
Also, a circuit diagram is not really an answer to my question. Maybe we would both be best served if another mechanic took over with the question.
Expert:  Chris (aka-Moose) replied 2 years ago.
I can opt out and let another help you, but since your post was started on the 1st, and its the 26th. Your post will be so far buried down the list, its most likely no one will ever see it, but I can opt out, being thats what you want. best of luck.
Expert:  Gary replied 2 years ago.
Hi there,I've looked at the circuit.If you have a high mount stop lamp and no brake lights in the body, then I'd say the "vehicle stop fuse 15A" in the left i/p fuse panel (instrument panel) is blown.Leave your trailer disconnected. If the above fuse is blown, replace it and see if the vehicle now has all brake lights. The CHMSL (centre high mount stop lamp) has it's own fuse, also in the i/p.Then if you hook up the trailer, and the fuse blows, the fault is in the trailer.Gary
Customer: replied 2 years ago.
Fuses are ok. Trailer is brand new and as I said previously trailer turn signals work fine and these are the same trailer wires that operate the brake lights.
Trailer brake lights went out first. I disconnected the trailer and later noticed cruise control would not work. Don't know when it actually went out.
About a week later truck brake lights went out.
Expert:  Gary replied 2 years ago.
I would go back to the trailer manufacturer.Clearly it is not wired correctly for your car.The circuit looks simple enough, if the CHMSL is working and the other stop lamps aren't, there are two fuses in parallel for the two stop lamp circuits, are both fuses live ON BOTH SIDES of the fuse with the brake pedal depressed? If they are, follow the circuit until you find the open circuit, Page 3 of 3 from above.Are all the rear lamps dual filament bulbs and fitted the correct way around in the sockets?Gary