[buzzinhalfdozen]

Bob ,yes I know however if the ground for the pigtail or socket is not connected it may be trying to find another path to ground.depending on the bulb and socket design it may be grounding back thru the filament in the bulb hence backfeeding another circiut since the tail and turn lamps are on completely different circuits.I've even seen some people put a single contact I believe 1156 bulbs in dual contact sockets and cause the same sort of issue. Joe Oh and one other thing I see alot of ,when guys wire plugs a single stray wire touching the adjacent terminal can cause this issue. Sorry don't mean to confuse you just hard to diagnose not being there.I also neglected to ask, do the trailer brakes work? If so I doubt you have a grounding issue as thet use the most power of anything on the trailer.