Larry, as stated above, British Wiring are the people to use for any wiring problems. They are really nice people, the wife is a Brit and will help you with anything you are having a problem with. (They are the secret source for most if not all of the harnesses that TRF sells "from England".) A couple of things: remember that many of the light sockets use the fixture housing as a ground source so make certain that these areas are clean and the fixture snaps in with authority (as noted in an above post). TR6 tail-light fixtures are famous for losing their grounds. I have resorted to both soldering the light fixtures themselves (I think Buckeye Triumphs has a tech report on this, may be archived.) and grounding the fixture with wire to the body. Another tip is to buy the bullet connectors from British Wiring along with the special crimper they sell. Expensive but priceless! ($50) I crimp and solder all bullet connectors, very original and an excellent way to make good wire connections, in spite of all the bad press that "the Prince of Darkness" has gotten. I digress but another excellent tool to buy is the snap connector from King Richard (on the web) that automatically and perfectly makes up snaps for tops (hoods), tonneau covers, underwear, or anything else you might want to make up using Dot-brand snaps. Greatest tool I ever bought.
Bill