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Trailer Lights Not Working On Multiple Trailers With 2005 GMC Sierra 1500


Ive got a 05 gmc sierra z71 1500, when I hooked up my trailer lights werent working, I assumed it was my trailer wire ground. Or faulty trailer lights. Well I went to my buddies to try his trailer a direct 7 way plug. So when my front headlights are off I get brake on/ left right turn signal. And as soon as I turn on headlights it kills power nothing happens. I tried my trailer at night and only passenger side lights work with headlights on. Could I have a faulty 7 way female adapter?


Expert Reply:

It definitely sounds like an issue with your 7-way connection or the wiring that leads to it on your 2005 GMC Sierra 1500 Z71.

I recommend using a Circuit Tester # PTW2991 to begin checking the poles of the 7-way on your Sierra. First make sure to check your fuses and relays that are under the hood and in the cabin for any that are damaged. The circuit tester can help with that task as well. Once all the fuses and relays are checked begin checking the poles on the 7-way. If you find that some aren't working follow the wiring back to the connection behind the bumper. Test that wiring to that circuit as well.

If the issue is in the wiring after that connection the Replacement 7-Way # C55774 can be used to fix your issues. If there are still issues continue to follow the wiring towards the front of the vehicle looking for any damage to the harness. If you don't see any issues than at this time is left best to the professionals to check the wiring continuity to determine if there is a wire that is damaged internally.

expert reply by:
Gregory M

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