My customer brought me a pair of back up lights to cut in his 68.I did that with no problem but now am wondering where to tie them in so that they work when backing up. The car was a standard 68 that he has installed a 350 and auto tranny. It originally had a standard tranny in it. He purchased an original wiring harness to replace the worn one in back..I am assuming the one that came with cars that had back-up lights had a slot to connect to. If I want to hook them up regardless of which harness I have how would I do it? Thanks

All 1st gens have backup lights. Non-RS equipped cars had them in the tail light housing and the RS cars were under the bumper. Either way there should be wiring in the trunk for them...

Sounds like you installed RS reverse lights, for which the pigtail penetrates the trunk very close to the tailpan brackets (there should be a dimple there). Anyway, the RS rear light harness is different than a standard rear light harness. The RS harness has extra connectors for the backup lights and the two push-in sockets for the rear bezels on each side have the same colored wires going to them. On the standard harness the inner push-in socket is single pole for that reverse light location in the rear bezel. You either need a RS harness, or you need to splice and reconfigure the wires and get two pole push-in sockets to replace the old single wire sockets on the inner side of the rear bezels.