7-Way Trailer Connector has 8 Wires and Brake Lights do not Work

Question:

I have a 7 pin diagram but I have 8 wire cant get my brake light to work

asked by: Cathy D

Expert Reply:

On a 7-Way trailer connector the brake lights and turn signals are on the same circuits. The pins in the connector at the 3 o'clock and 9 o'clock positions are the turn signal and brake light circuits. On the tow vehicle side use a circuit tester such as # PTW2993 or a meter if you have one to test those pins while someone sits in the vehicle and steps on the brake pedal. If there is no power on those pins during this test, then the issue is on the vehicle side and is likely a blown or missing tow package fuse or relay.

If it works right on the vehicle side, then the issue is on the trailer. Since brake lights draw constant power, the issue could be a ground problem. Ground problems normally show up when there is more draw on a system such as when you have the running lights on and then use another function like a turn signal or brake light but can show up any time.

Make sure that the vehicle side and trailer side connectors are clean and free of corrosion inside and out. The main connector grounds should be attached to clean and corrosion free bare metal surfaces.

The light grounds should also be attached to clean and corrosion free bare metal surfaces. If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding tongue, any of these things can interrupt the ground. Running jumper wires from the light grounds to the main trailer connector ground can help.

The fact that you have 8 wires could mean that you have 2 running light wires, one for each side of the trailer, so you don't have to run a jumper wire from one side of the trailer to the other.

expert reply by: Michael H