Tailight wiring harness/74 duster

I have a 1974 duster, trying to finish wiring, i put a 1971 duster dash wiring harness to get rid or seatbelt interlock, my wiring under the drivers kick panel has a gray wire, coming from the rear harness and in trunk it has a single push on plug , that i have no ideal where it went, and on the 1971 harness that plug at kick panel ,doesn't have a gray wire, and my gray from under dash matches the green wire which goes to rear wiring harness when plugged in, but on wiring schematic diagram, shows green wire goes to bulb sockets. I dont have a green wire in tailight harness, Any input would be appreciated.