Trailer Brake Lights Do Not Work on Trailer Towed by 2004 GMC T7500

Question:

I have a 2004 GMCIsuzu T7500. New 7 flat pin connector on truck hooked to new trailer. Have all light and brake functions except brake lights on trailer. No power to yellow and greenL and R turn signal wires with brake application. what am I doing Wrong? Do I need a converter? What is a converter and what does it do?Thanks

asked by: George W

Expert Reply:

It sounds like 1 of 2 possible issues. First, if the vehicle has separate turn signal lights from the brake lights then you have a 3-wire system and you would need a converter such as # 119178KIT to take the separate signals and combine them. Then you can run the combined signals to the 7-Way by cutting off the 4-Way of the 119178KIT and attaching the wires to the 7-Way.

The other possibility is that if the vehicle has combined brake and turn signal lights, the stop light/CHMSL fuse may be blown. You would use the vehicle owners manual to find the fuse location and check it.

I have included a link to an FAQ on trailer connector diagrams that should help.

expert reply by: Michael H