Troubleshooting a 7-way Connector on a 1998 GMC Truck

Question:

I have a 1998 gmc that came with a 7 pin, 6 around and a large cent pin. I cant get it to work with a 4 pin trailer set up . i think the original owner, im the 2nd, had it wired wrong it is as follows as looking at it from the outside 1-oclockorange 3-oclock- green 5-oclock-blue 7-oclock-white 9-0clock-yellow 11-0clock-brown and nothing on the center pin. i have the adaptor for the 4 pin, green,brown,yellow,white. if you have my solution i would appreciate it. thanks

asked by: Dave P

Expert Reply:

Traditionally 7 way vehicle connectors are wired as follows:

1:00 Black, 12 Volt Battery Power
3:00 Green, Right Turn and Brake
5:00 Blue, Brake Controller
7:00 White, Ground
9:00 Yellow, Left Turn and Brake
11:00 Brown, Tail and Running Lights
Center Pole is usually a Purple wire that is run to reverse lights

It sounds like your vehicle connector is wired by function correctly, but there could be a problem with some of the wiring at the connector.

You are going to want to use a Circuit Tester, like part # PTW2993, while a friend is in the cab of your truck is applying the brakes, blinkers etc. while you use the circuit tester on the appropriate pole of the back of the connector of your truck to determine if there is a problem in any of the circuits on the truck side of the circuits.

If everything checks out there you will want to repeat the process on the front of the connector to determine if the problem is somewhere in the connector itself. Next, you would want to repeat the process again with the 7 way to 4 way adapter you have, and finally, if that all checks out you will want to look at the wiring of your trailer for any possible bad connections that might be preventing your trailer lights from working.

I have link below to a trailer wiring FAQ that you might find helpful.