my motorhome has two dome lights that are inop. the bulbs are good. how do i diagnose from here?
Motorhome wiring can be a mess, depending on who wired it. Start by looking for fuses that are bad. Next, you can take one of the bulbs out, and check which side of the circuit you lost (negative or positive). This can be done with a cheap mutlimeter, or test-light. Odds are that you lost the positive side, because most dome lights use a "body ground". But not always. If they mounted these lights on a surface that is not connected to the steel body of the vehicle, they would need to run a body ground circuit/wire to it. How do you know what side is +/- on a bulb? I screw in, or 1/4 turn screw in bulb has a copper base, which is negative. The little nub on the bottom of the bulb, is the positive connection. If the motorhome manufacturer is still in business, you can request a wiring diagram from them. Hint: it may not be Ford wiring. Can you take a pic and post location of you dome lights? I could tell you more about them, if I saw where they were mounted.
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