12V lighting and LEDs
Most RV lights are 12V LEDs. They fail differently from old bulbs: polarity matters, and flicker or dimming usually points to the supply, not the fixture.
The short version
- Many LED fixtures only light with the polarity right. A new fixture that's dead may just be wired backwards.
- Flicker or dimming when other loads run: check voltage at the fixture under load. It's usually a ground or connection.
- One fixture out: test voltage at that fixture. A whole area out: check the fuse, the switch or the module that feeds it.
- Some cheap LED bulbs flicker on dimmers made for old incandescent bulbs.
- On multiplexed coaches, lights switch through modules. Several unrelated lights quitting together points at a module.
Shop tip
Carry a known-good fixture. If it lights on the circuit, the old fixture is bad. If it doesn't, chase the wiring.
Try it on a service call
Put the lesson to work on a hands-on troubleshooting case.