Greetings . . .

A wiring diagram would probably be the best way to figure this out.

The Old Car Manual Project only goes through '65:
TOCMP 57-65 Chevy Wiring Diagrams

Rock Auto has got one for five bucks:
Bishko Wiring Diagram for 66 Chevy II

regards,
stock49

[Linked Image from 49fastback.com]