I've had an odd one like this. The pigtail fro, my wife's Mazda plugs into the trailer, but the Ford style plug doesn't fit the Westin module all that well, so I cut all the wires, and just manually connected them. Brown to brown etc. When I plug the mazda into the trailer all works except the running lights, ie the taillaights, brakes and turn signals come on just fine. When I plug it into the Ford Explorer everything works as normal, so that tells me I may have an issue with the Mazda connection on the taillight. Yours is a probably similar situation, as if you've done the new wiring, it's either in the bulbs or the wiring load.