did they work at first or did you lose them after connecting a trailer? do you have a multi meter?
I would check the ground for the BCM, G104. Shows it by the firewall near the master, left rear of engine compartment.
Make sure f70 and f100 are good in the BJB(battery junction box)
they power the reverse, left and right lights
check f28, F55 AND F90 too
use the meter to see how many volts