I will probably go with a generic buzzer. It is strange it is not shown on any of the diagrams. I found it in the assembly drawings called out as Buzzer warning unit 377595, and I have found the circuit in an 77 Vette electrical troubleshooting manual I had bought when I first got the Vette. This is a good book it shows all the circuits and the location of components and grounds. The Buzzer unit controls the seat belt light, key buzzer and of course the headlights warning. Looking at some old threads I believe this was a source of battery drains. I guess I will spend a little time seeing if the part is available then proceed. So the question is answered 77 does have lights on warning and now we know were it comes from.