Troubleshooting Common Trailer Wiring Issues on 2004 Chevy Suburban & 2006 Cadillac Escalade

Question:

I have a 2004 Chevy Suburban and a 2006 Cadillac Escalade EXT and both do the same thing when hooked to a trailer. The left turn signal and brake light do not work. I have used different trailers, adapters, checked the fuses and grounds and it always comes up the same thing, the left blinkers and brake do not work on the trailer. the running lights work. I have spent some money and time trying to figure this out and am stumped. I dont understand why it is just the left side that does not work, it cant be the trailers I have used since It does the same thing on every trailer 4 I have used, and I dont think its the vehicle since it is doing the same thing on 2 different vehicles. And finally i dont believe it is the adapter since I have tried 4 different ones with the same results. Am I missing something or am I just stuck with this predicament?

asked by: Jim M

Expert Reply:

That's a tough one, indeed. Usually, we can isolate the cause for a wiring problem by substituting an alternate vehicle or trailer.

My initial suspicion is that both vehicles have a ground problem. A weak ground will allow some lighting functions to work while others may not. I suggest you check the white ground wire for each vehicle's wiring harness to ensure these are tightly affixed to a clean bare metal spot on the frame. If the grounding points are rusty/greasy clean and sand them to expose bare metal and re-attach the ground wires using an application of protective dielectric grease # 11755.

Once you do this you can use a circuit tester like # PTW2993 to test the vehicle connectors for the proper signals without any trailer connected. Please refer to the linked video for illustration of the testing process. The linked photo shows you the pin functions. If the correct signals are present on the vehicle connectors, then this tells us that the issue is likely to be in the adapters or in their connection at the vehicle. (The odds of 4 trailers all doing the same thing wrong is pretty unlikely.)

You can also check the condition of the pins on your 7-way sockets to ensure there is no discoloration or corrosion on any of the contacts.

expert reply by: Adam R