I'm doing a on frame restoration of a 74 Vette (my first vette) and can't figure out from the wiring diagrams I have what the interlock under the hood with the start button does. It's attached to the ac/heater housing. I'm was thinking it is for the seat belts, but that doesn't seem to make sense. It's driving me nuts. Please help improve my sanity.

If your talking about that little switch up on the cowel near the wipers that is suppesed to push down when the hood is closed,that is part of the alarm system.which probably doesn't work anyway not very many of them do .they were very prone to failure,there should be 2 more switches just like that one in the rear door jambs,they are probably coroded or broken

I actually got the alarm system up and running. It sounds pretty sick and probably won't scare a theif, may make him laugh. The interlock I'm talking about is about 8" to the left of the hood alarm plunger switch. It is about 2" x 1" x 1 1/2" with a black button coming out of the center with the word "start" under the button. It looks like a relay with a button.

The '74 Vette was equiped with a seatbelt interlock that would not allow the car to be started without first fastening the seatbelt. The button under the hood is a bypass that would allow you to start the car if the interlock system failed.

If you are able to start your car without fastening the seat belt then I suspect your system has already been disabled. The cutting of a single wire near the fuse box is all it takes to eliminate the interlock.

Thanks, I appreciate the info. Don't plan to go as far as refurbishing the seat belt interlocks.