I have an issue with the backup lights on my c10. It is a 3 speed on the column. I have replaced both bulbs now and I have 12 volts coming thru both sides for both bulbs. the backup lights will come on as long as the bottom part of the sockets are grounded. It is only the socket being grounded and not the rest of the backup light body that will allow them to turn on.The bottom appears to be copper unlike the rest of the socket. I cannot figure out what the bottom of the socket would come in contact with when it is screwed in place to allow it to touch something to ground it. Am I missing something here??? I thought about just buying new sockets but these work when they are grounded. Is there somewhere on the sockets that need to be clean that i am missing Thanks, Chris