Wierd Tail/trailer light issue

[Eggman]

Was having issues with the trailer lights, so they were rewired with 16 gauge wire with no problems. Function check, all is good. Went to hook up some reverse lights on it, power from the reverse lights on the truck, function check, all is good. Couple of days later.....all of the trailer lights go out completely when the truck is put in reverse. Doesn't matter if its running or not. Wiring has been checked and double checked. I am at a loss for an explanation. Any ideas?

Thanks In Advance.