No power to backup lights

[EMD360]

We noticed the left backup light was out but the right was functioning. It was not a bad bulb. I pulled the socket and disconnected it and had no power to the light. Water was definitely getting into the light socket as there is some rust on it and the cavity was wet. It looked like the rubber gasket still had the protective paper on the coach side! I thought that somehow I might tap into the power to the other light so I disconnected it and blew the fuse at some point. I reconnected it and replaced the fuse but it still doesn’t light. I read that there is a reverse switch on the transmission but I don’t see reports of that going out on a 2018 model. I’m not sure I can find the switch as I’m not finding a late model E350 diagram to see where it is located. All this is a pain because it’s reverse and so to keep from being run over someone has to be in the driver’s seat in reverse but on the brake with the emergency on. Any hints will be appreciated.

[Grit_dog]

Nothing illegal about not having backup lights since you don’t use them on the road.

[EMD360]

Also since we are going camping this weekend and I was worried the problem would not be fixed, I read that it is legal to drive without backup lights. Never knew that.

[EMD360]

I suspected the wiring but I think it was a corroded socket. Laugh if you must but the multimeter I was using was an old cheap one from the rv. I decided to test it on the engine battery and it blew up! Yes it showed 0.00 at turn on and I’m sure I had it set correctly. So there it was. I just needed a night to stew about it. So I cleaned the contacts with sandpaper and reinstalled it. Somewhere in my testing the second bulb stopped working but I think it’s also just corroded. I just put in the second new one and now they both work! Seems the lens gaskets could be replaced or at least caulked.
The information about the bulbs turning on without the engine running was invaluable. I realize I should have known that from testing trailer lights. Sometimes it’s the brain that’s mis-wired!

[Dusty_R]

It's the same filament in the bulb as the left turn light and the emergency flasher. So if they work, then it's not the bulb but the wiring.

[DrewE]

EMD360 wrote:
All this is a pain because it’s reverse and so to keep from being run over someone has to be in the driver’s seat in reverse but on the brake with the emergency on. Any hints will be appreciated.

I don't know that I have much to offer on the electrical problem (other than the usual things to check)...but you could safely test the backup light by putting the key in the run position without starting the engine, setting the emergency brake, and shifting the transmission into reverse. Unless you're on a pretty steep hill, the RV definitely won't move. Put down some chocks to be doubly certain if you wish.