Trailer reverse light wiring

The problem I see is there is no way for the trailer to know it is in reverse, as the truck does not communicate with the trailer, and the abs wheel speed sensors are only passive sensors.

I think you would either need a separate switch and a hardwire connection between truck and trailer, to be able to flip a switch from the cab every time the trailer was in reverse, or a separate signal conditioning box, along with an additional or special wheel speed sensor, to signal the trailer was reversing, in order to achieve the automatic reverse lights.

Does anyone else know of any other ways?

 

Easy peasy

2nd plug to trailer, wire in another relay on the tractor's reverse light circuit. Boom! Trailer reverse lights any time the truck is put into reverse.

 

FWIW, I was talking to a step deck O/O a few months back, on his headache rack, he had 4 work lights on adjustable poles for tarping/strapping at night. On the trailer he had 6 aux lights, 2 on ea side and two in the rear, they were back up lights. He had a separate power wire taped to his 7 way, that connected to an extra harness on the trailer, then in the cab he had two extra switches on the dash, one for the work lights, one for the trailer lights.