Phil, Do the lights work correctly on the trailer by themselves using the switch on the control panel?
If they do, then the issue is probably in or on the "Brain" box DRV installs that runs the turn signals, brake lights, etc. As long as the truck side is working correctly then that's where the issue is.
BUT
Since you just had a bunch of work done, whats the chance there is a rubbed/burned/snagged/stray thread of a wire not in the right place at the truck receptacle? If not call Slade at RR.