[mrein3]

Red - 12 volts with key on.
Green - "Tach" connection on HEI or "-" side of coil if you still run your points distributor.
White - goes to the dash lights wire - usually a gray wire on this vintage of Chevy.
Hooking it to your gray wire will allow you to dim the tach light with the rest of the dash lights. The gray wire that goes to the light behind your heater controls is a safe bet.
Blacks - Chassis ground.