Trailer Lamps Work Fine Until Vehicle Headlights Are Turned On  

Question:

Expert Reply:

You're having a ground problem, what you describe are the classic symptoms.

When the vehicle headlights are switched on, the maximum amperage will be drawn through the system which is when the problems show up.

There's a few specific areas you'll want to check.

1) Make sure the trailer connector socket on the tow vehicle is grounded to the vehicle frame or chassis,
and that the connection is tightly made to metal that isn't rusty.

2) Make certain that the main trailer ground which is usually on the trailer tongue is securely connected to
clean metal. To find the ground, simply follow the white wire rearward from the trailer connector.

3) Each trailer lamp will have its own ground connection, either by a separate wire connected to the trailer
frame or by having the lamp's housing being in direct contact with the trailer frame. Make sure these
connections are clean and secure.

4) The basic design of some trailers can contribute to ground problems. If your trailer has a tilt bed or a
swinging or tilting trailer tongue, the pivot points between the tilting or swinging and the stationary portion
of the trailer can become worn over time, and fail to keep a continuous ground connection. This can be
repaired by taking a length of wire long enough to connect the moving portion of the trailer to the
stationary portion without hindering its movement. Install a ring terminal like # DW05702-1 on each end
and use a self tapping screw to join both parts. This wire will act as a jumper connecting the stationary
and moving portion of the trailer, keeping a continuous ground connection.

Existing grounding points to the vehicle frame/chassis or trailer frame can be cleaned up if they're dirty or corroded. If you simply shoot a self tapping screw through a painted surface, the only ground connection you get will be through the threads of the screw which is pretty minimal. However, if you remove the self tapper, sand a 1/2 inch diameter area around the screw hole down to bare metal and install a star washer between the ring terminal and the trailer frame, the washer will bite into the metal surface, giving you much better metal-to-metal contact for a more reliable ground connection. Once fastened, protect the connection with a quick shot of rust inhibiting spray paint and you'll be good to go.

expert reply by: Mike L

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