1970 roadrunner

1 black wire....plugs into windshield wiper motor connector
1 black wire(white tracer) also plugs into same connector, but it also has another 5"
or so piece that plugs into terminal Z (engine harness plug)
which does what inside the car???? my wire diagram shows nothing

When I spring for the $100 dash mount reverse light(its a 4 speed conv. car) maybe this will be more clear

Looks like I might get 1 week on the road this year, almost done...5 + - years in build
Mike

on the inside of the car, the black with white tracer wire continues from terminal "Z" directly to the reverse indicator light. there is a short purple ground wire that screws to the dash frame from the light.