bulld

No upgrades or bulb changes, so look for a ground fault?

cihmagnum

Unless someone here has a better idea. The bed lights is kind of a give away for me. You can turn them and the cargo lights on the third brake light on the same time at the switch in the cargo box, but that switch does not control the backup lights at the taillights or the third brake light. Are the license plate lights coming on also? If you hit lock key, which lights actually light up? Have you taken this truck through a car wash lately or had any heavy rains? Moisture in the third brake light housing has been a known issue for some here.

16IngotFX4

No worries, it was confusing trying to determine any causes. If you had a reverse circuit connected to the high mounted light I'd be concerned somebody may have altered the wiring.

The switch inside the bed, on the left side near the rear, is probably bad. It pops out fairly easy I believe.
I think others can help with that part of disassembly (I can't remember exactly), but that fails fairly often.
Somebody replaced the switch a few weeks ago, they sourced the part at their local parts store if I recall correctly. In the meantime, if you can get the switch removed, you can disconnect the electrical connection. As with any electrical connections, use caution not to break the locking clips (they get finicky and sometimes brittle).
I didn't realize the backup camera light is part of that. We can let others explain.

I think @52merc has a diagram of the switch and how to remove it.

Here is a thread to see a photo of the switch
https://www.f150forum.com/f118/3rd-b...ndomly-472344/

I have a link there as well in post #3.... a similar complaint to yours as 'reverse lights' -see if those threads are the same as your experience.

Wexford F150 Owner

I once had my LED bed lights in the 2015 XLT go on and off spontaneously. This went on for a few months. After a couple of days at the dealer, they found there was a switch that was corroded and causing a short. But, in my case, no other lights were affected.

bulld

Please tell me it was the bed switch, that's the easiest to get to.

Wexford F150 Owner

Yes it was the bed switch.