After Installing LED Trailer Tail and Clearance Lights Only Turn Signals Work

Question:

I installed two STL70RB taillights and 4 MCL95RB clearance lights on my boat trailer. I also put in new grommets and purchased the 3 wire plugs for the taillights. I attached white to ground, red to red and black to black to match the previous lights that were in the trailer. When I tested them after the install the directionals work great but when I turn the headlights on nothing works, no taillights, no brake lights, no directionals and no clearance lights. What did I do wrong. The old lights were incandescent and worked fine.

asked by: Gene C

Expert Reply:

It is not likely that the clearance lights, # MCL95RB, are the issue since they ground through the mounting hardware and only have one power wire that goes to the running light circuit. Still it is worth checking to make sure that the grounds are attached to clean and corrosion free bare metal surfaces.

On the taillights, # STL70RB, the red wire is for brake lights and turn signal, black is for running lights. And white is the ground. You can't always go by color; you have to go by function. I recommend testing the trailer wiring with a circuit tester, such as # PTW2993, to make sure the wire colors on the trailer match the functions as indicated above for the taillights.

Otherwise, this sounds like a ground issue. 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.

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.

I have included some links that should help you.