From the F100 Website forum:
"
Door jamb sensor on 1972 F100
Sorry guys I didn’t see this post earlier. Art is right, that is an ambient air thermal sense switch for the emission control system. Lighter duty trucks and all cars from that time period were saddled with this system. The thermal switches are similar throughout the years but the control system that it is hooked up to went through several names and changes.
Basically the system controls emissions by NOT allowing any vacuum advance to the distributor unless the vehicle is moving at least 25 to 35 mph OR the outside air temperature is below 50 degrees. The earlier system used a speed sensor spliced into the speedometer cable and an electronic control module with a solenoid valve. The later system used a transmission switch to signal high gear and an electronic amplifier with a modulator valve.
I can help you troubleshoot the various evolutions of this system if needed.
Not very exciting after all.
Barry"
And also a link to the thread:
https://www.ford-trucks.com/forums/7...tml#post494508