Trailer Lights Malfunction on 2007 Ford F-150 Towing a S and H Horse Trailer  

Question:

Expert Reply:

The first part of the problem sounds like a bad ground. A bad ground usually shows up when the system is under load. Start by checking the trailer and vehicle side connectors. Clean out any dirt or corrosion built up inside and in the backs of the connectors.

Next check the ground on the vehicle side connector. It should be attached to a clean, bare metal surface on the vehicle frame. Also check the trailer side main ground. It should be attached to a clean, bare metal surface on the trailer frame.

From there, check the grounds on the trailer lights. If there is not an obvious ground wire on the light, it probably grounds through the mounting studs. In either case the lights, too, will need to be attached to a clean, bare metal surface.

Since your 2007 Ford F-150 has a combined system (turn and brake lights), and you turn on the headlights and activate the right turn signal, there is most likely a short that is causing the brake controller light to come on. The current is being fed back to the brake wire connection instead of the turn signal.

With all of the grounds checked, you can then look to see that the wiring on the trailer is physically intact. First looking for any obvious brakes or nicks in the wiring and repair as needed. You can then check the entire length of the trailer wiring by periodically testing the wires with a circuit tester, part # PTW2993, to locate breaks you cannot see. You can also do this on the vehicle side if you determine that power is not making it to the trailer.

expert reply by: Jeff D

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