Starter Seatbelt Interlock Relay
 

My 1975 911 Carrera is an October 1974 build and was equipped with the 1974 federal mandated starter seatbelt interlock system where the starter was prevented from cranking the engine if the seatbelt wasn't fastened.

That system had been defeated long before I bought the car (in 2006) by disconnecting the seat sensors - if the seat is empty, then the seatbelt doesn't have to be latched for the starter to crank when the ignition switch is turned to the start position.

But my car is now 50 years old and I thought if that interlock relay fails, I won't be able to start my car. So first I removed the interlock relay and confirmed the starter doesn't crank when the ignition key is turned to the start position.

Next I reviewed my wiring diagram to see that on the interlock relay pin C goes to the ignition switch and pin 50 goes to the starter. Then I made a wire jumper out of two 16 gauge yellow wires (correct color, wire size I had in my tool cabinet) with a 1/4 inch male blade connector on each end (I used two 16 gauge wires to approximate the current capacity of the 12 gauge wires used up to the pin C and pin 50 terminals of the interlock relay socket). Finally, I plugged the wire jumper into pin C and pin 50 of the interlock relay socket and verified the starter cranks when I turn the ignition switch to the start position.

Interlock relay and wiring diagram:

http://forums.pelicanparts.com/uploa...1761050521.jpg

Wire jumper in place on the interlock relay socket:

http://forums.pelicanparts.com/uploa...1761050601.jpg