my truck did the same thing. it would have 12v at the conector but with the bulb in. the voltage would drop like a brick to like 2v. i made a relay for each power wire and used the 2v. out of the old harnes as a signal for the relay. it worked. i used two fog light relays. getting power from the battery. use a fuse inline with your power wire will save you a melt down. lol...just an idea..