Beginners Guide to RV Wiring

First - check the ground.

Next:

The running lights can be a constant source of trouble, especially on aging RV's. The electrical connections are subjected to varying degrees of temperature changes, humidity levels and road vibrations. This leads to a build up of corrosion on the contact areas and frequent light outages, which always seem to crop up at night (naturally). And most often when it's raining, windy or otherwise nasty.

A short circuit can be caused by wires that are constantly rubbing against the frame or other metal object. A screw or staple, inside the walls or ceiling, may have punctured the wire. Have you added any accessory on the coach that may have put a mounting screw though the wiring? Once the insulation on the wire has worn away, the circuit shorts to ground and the resulting high current flow blows the fuse.

Finding the problem involves a step by step investigation.

The clearance lights are wired in parallel - there should be a "hot" wire and a ground for each light. (Some coaches use the metal skin as the ground path - others have a separate wire for this purpose.) The power wire connects to the light and also carries on to the next light in the circuit. Usually it is the green wire that is the hot wire.

Disconnect the power source ...

Remove the trailer plug from the tow vehicle and disconnect the trailer battery ...

Remove the cover lenses and the light bulbs from every clearance light and both tail lights.

Start with one of the front side clearance lights, assuming that they will be first in line. Remove the mounting screws and pull the light away from the wall to access the wiring behind it. Disconnect and separate the hot wires that lead to that light.

With an ohm meter, test the wire that leads from the power source (trailer plug) to that light. The negative probe of the meter is touched to a ground source and the positive probe to the bared wire end.

If the meter shows continuity on that wire, that's the faulty run. If that wire shows no continuity, test the wire that goes to the next light. If that wire shows continuity, leave the light disconnected and continue to the next light and repeat. If the wire that runs between the lights is shorted, the meter will show continuity. Keep going untill you isolate the shorted run. Hopefully it's in the first few lights.

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