1972 does not turn over when hot

[franken]

Like I said, fixing the wiring is the solution, not adding another solenoid.
Measure the voltage to ground at the S terminal of the solenoid. It will be low causing the solenoid to not work. Trace the purple wire back and fix the issue.
The ford solenoid switches the starter cable as well, for no particular reason on a Delco starter.
I bought a truck that had 2 horn switches, 2 ignition switches and a ton of 12AWG red wire because it seems the PO also didn't want to spend time solving the actual problems. Same concept w/ ford or other extra solenoids.