I am in the midst of recovering my dash, and I started thinking about the Fasten Seat Belts Light in the middle. When is that supposed to come on? When you turn the key on? Is it timmed to turn itself off like a modern car? Mine never worked, so I would like to know how and when it should come on.

Well I hated those things (seat belt lights and interlocks) when they first came out. I think it would be quaint to have one that functioned. My recollection is that the light and buzzer would come on when the key was turned to its first stop, and turn off wheen the belt was fastened. No timer or other modern "technology".

It's tied into the relay under the passenger seat.

I believe it stays on if the pressure switch in the seat is open (someone sitting in it) and the seat belt buckle isn't latched.

So, how could it be set up to blick or flash a bit, then turn off, without being tied to the seatbelts?

Mine is a '73 and it buzzes and lights up when:

1) car started or key at start position, parking brake off seatbelt unbuckled.
2) car started or key at start position, parking brake on, door open

Its my understanding that earlier cars were different. YMMV