The latter part of your statement is true. The barrel of your socket should provide the ground whether it be through the housing's connection to the body or a seperate ground wire.
Edit: on the early cars there is a third wire for ground in addition to the two prong plug.
glad you figured it out bro....I work on wireing in helicopters, so I understand how frustrating it can be....try working with about 200 miles of wire, ranging from 22 GA, to coax...lol
damn man, i should have thought about that, i knew that the signals ground to the bumper because i had a problem years ago with mine not grounding correctly and popping the bulbs. it was an intermittent issue though and totally different than what you had but still ground related. i knew it was a ground issue though, that was the only thing it could have been, i just wish i could have remembered about them grounding to the bumper. anyway, glad you got it figured out!!!