The Ground Circuit
The ground circuit is the first thing to check and repair if you have a wiring problem. The electrical current needs a good return path from all the other circuits in order to allow everything to operate properly. Depending on the trailer hitch to provide this return path DOES NOT work!
To establish a good ground, thoroughly clean or replace the connections and grounding screws on both the tow vehicle and the trailer. You will have to follow the ground wire (white) from the plug or socket back to where it is attached to the frame of either vehicle.
The ground connection is so important that I'll have to repeat myself here - make sure your ground connection is sound before proceeding with your trouble shooting - the ground probably accounts for 50 per cent of wiring failures!
Don't assume that because some lights are working, that the main ground is okay - some circuits will feed back through other circuits in an attempt to find a ground. If some strange things are happening, lights that aren't supposed to flash are flashing etc., it is most likely a bad ground problem.
Older coaches with metal siding often relied on the trailer "skin" to provide a return ground path for the electrical current. This ground connection was provided through one of the light mounting screws. To see if your coach is wired in this way, remove one of the running light assemblies and note the color of the wires behind it. If you have one or more green wires and no white wires connected to the light, you most likely have this type of lighting circuitry.
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