Seat belt interlock.
If the car runs with that unplugged it's been bypassed under the passenger
seat.

Ah ok, thanks!

So a seatbelt interlock disables the car unless a passenger has put their seatbelt on correct? And bypassing renders that system useless?

Driver or passenger. There is also a pressure switch in the seat that interlocks with the seatbelt. I have never seen one that still works.

So, a few weeks ago I had the seats out and re-connected the two plugs. To my surprise the "fasten your seat belts" light lit up. But when I turned the key, nothing. Engine did not turn over. I un plugged them and the engine started right away. Just for clarification. If I would have buckled my seatbelt, the engine would have started??

I have a 74 1.8

Thanks fellas.

Maybe. It should have.

With everything connected correctly and functioning, the seat switch needs to be activated (sit in the seat), buckle the seatbelt, and turn the key. If something is amiss the engine will not start.

If for instance you put a heavy box on the passenger seat, and the passenger seatbelt is not connected, the engine will not start.

The system works on my 1974 914, I have not disabled it...but I do carry a splice connector in the car for the big yella wires just in case.

unpicked my lower seat bases and took these strange sensor thingies out last year really don't want to carry that junk around.

Thx Jeff