What Causes Trailer Running Lights To Light Up After Trailer is Disconnected

Question:

How is it possible that my trailer running light comes on when my trailer is not connected to my truck but I have my on board battery chargers are plugged in and charging?

asked by: Danny F

Expert Reply:

The only way for the trailer lights to illuminate while the trailer is unhooked would be a short-circuit. The short is occuring between the light being illuminated and a constant source of power like an on-board battery. The short could occur anywhere the wires are close or touching. The running light circuit is usually carried out on a brown wire, I first recommend checking the trailer connector for corrosion. If there are no issues here you'll need to start tracing the running light wire back from the trailer connector to the taillights looking for shorts along the way.

If the trailer connector is too badly corroded then it will need to be replaced, part # 18004 for a 4-way or part # H20043 for a 7-way. If the wires are too badly mangled then you may also want to consider replacing the harness as well, part # 16-4B-1 for 4-way or part # DW04914-1 for 7-way which are sold by the foot.

expert reply by: Conner L