Towing Issues: brake lights, 4x8 utility trailer, plymouth sundance

Question
don    i have a small 4x8 utility trailer that i'm attempting to hook up electrically with my 94 plymouth sundance. everything seems to work fine [directionals, brake and running lights]. my problem is that when i have the running lights on and hit the brake pedal my trailer lights go out although the brake lights on the car work. if the running lights are off, the trailer brake lights seem to work fine as does the car brake lights. i'm losing sleep over this and want to take my boat fishing. please help. the wires are new that i just put on, it didn't have any wiring before.

Answer
Sounds like a bad ground somewhere.  That is 99% of all trailer wiring problems.

Best advice I can give is double check your wiring starting with testing every connector on the Sundance and diagram which plug things are at.  Then diagram the trailer wires and one wire at a time with a jumper, hook up the vehicle to the trailer and see what happens.  

Be sure you have a really good ground between the Sundance and the trailer.  Don't depend on the hitch, run a separate wire.

Don