So the safety switch just completes the ground circuit. Not sure why there’s always a problem with them? Can’t remember if they’re adjustable or if it’s an issue with the tailgate not closing completely?
Relays usually have a ground wire going in. The mechanics behind a three wire relay (two hots going in and one hot going out) don’t quite compute unless it grounds through the housing.(?)
According to the schematic for 1972 the relay gets juice from the circuit breaker via the L (light purple/lavender) wire, and is triggered by the BY (black w/ yellow stripe) wire which forks off the ignition circuit between the ignition switch and fuse panel.
If there’s no voltage when the key...
I don’t know how much this will help you - I have a partial schematic pic for my 77 that shows the circuit. White wire with lavender stripe going to the circuit breaker.
It looks like 12v coming into the relay from the turn signal circuit.
I’ll post a better pic for the 72 year circuit when I...
I’d say yes. Check voltage at the switch on both sides, and then circuit breaker and relay, and so on until you know you have voltage from the switch to the tailgate.
So you’ve verified that the motor works, but now unconfirmed about the circuit coming from the dash switch? IIRC, the circuit passes through a relay AND a circuit breaker before heading to the tailgate.