1997 Chevy K1500 Trailer Brake Lights Go Out when Running Lights are Turned On

Question:

I have a 1997 Chevrolet K1500 pickup. I installed a 4-wire flat connector into the truck wiring harness. Everythings works great. I have verified the truck wiring with a plug-in tester and all is good! My trailer has a 4-prong connector with five wires including the ground. All the lights work. The brake lights work when the lights are not on. The tail lights work as expected with no brake applied. However, with the lights on, when you press the brake pedal, NO tail lights and NO brake lights! Any ideas?

asked by: Terry H

Expert Reply:

This is symptomatic of a ground problem on the trailer. Ground problems normally show up when there is more load on the system. Applying the brakes with the running lights on will be the maximum draw from the lights.

The connector on your trailer is a wishbone harness. It should have 2 running light wires, one for the left side and one for the right side. On a regular 4-Way harness there are 4 wires and the running light wire is split to got to each side using a jumper wire.

Make sure the ground wire is attached to a clean and corrosion free bare metal surface. Do the same for the lights. If there is no obvious ground wire then the lights ground through the mounting studs. You will also want to make sure that the vehicle and trailer side connectors are clean and free of corrosion.

If the trailer is a tilt trailer or has a folding tongue you will need to run a jumper from the light grounds to the main trailer connector ground. You may need to do the same if it is an aluminum trailer.

The 4-Way on the truck needs to be grounded to the vehicle frame. For a 1997 Chevy C/K, you should be using harness # 118315 . I have included some links for you that should also help.

expert reply by: Michael H