Electrical lighting circuit not working

[hughesjm21]

I went to Motorhome this weekend to check it out. I found one of my 12 volt ceiling light circuits would not turn on, all others worked. I removed the switch and disconnected the two wires. I checked continuity across the switch and found it to be open/closed as one would expect as the rocked was moved back and forth. I measured voltage across the two disconnected wires and found 3.3 volts.

I believe this means I have something wrong on the supply line to the switch. I also wonder if it could be a ground problem. All wiring is embedded in the walls except for switches and lights so I do not know where the various wire connectos or ground points are.

Any ideas would be appreciated.

[BB_TX]

I would use a long wire for an extended meter lead and check the voltage at the disconnected wire direct to a good ground at your fuse panel. If it has 12 vdc measured direct to good ground you know that part is good and the problem is downstream of the disconnected wire. If it has 3.3 vdc at that point you know the problem is upstream. Tells you which direction to start your search.

If your fuses have blown fuse indicator LEDs, the red LED on the fuse should illuminate when you turn the light switch on and the fuse is blown. Note that the indicator LED will only light up if the light switch is on as the indicator LED needs a path to ground thru the light bulb element.

[curt12914]

I would suspect a bad ground or, possibly, a faulty switch.

[wa8yxm]

Possible problems
Blown fuse
Burn Out Bulb
Secondary Switch turned off
Broken wire
Broken connection.
NOTE this last includes a failure ground side on the lamp

Oh and if you are still using incandescent lamps broken socket insert (Bayonet type lamps like the 1141) if that's the problem I can send you a repair kit I no longer need... If I can find it. NOTE the kits I have are NOT for sale.