Just for your information, While cranking a engine, full battery power is supplied to the coil from the starter solenoid. This insures maximum voltage during cold heavy cranking. Once the engine starts and the key returned to run, voltage from the switch is routed through a resistor, (could be firewall mounted or built in wire). The resistor knocks the voltage down to 8 or 9 in a 12 volt system. The engineers designed it to run at this lower voltage for longevity and parts wear.
When HEI came along, it needed full voltage all the time so the resistor circuit was removed and the key switches revamped. The starter no longer supplies voltage during start, the key switch does. The late model key switch has a start and run contact tied together and one 12 gauge wire to the HEI.
You can make yours work by still using the starter solenoid wire and key switch. There is no need for a relay, although its a good idea. It sounds like is your relay is dropping in the run position.
A simple test light will prove out the key switch, just find voltage in run position and use it to trigger your relay. For start, use the factory wire all ready run to the coil and tie it to the new HEI wire or back at the relay. It may skip a beat when the relay jumps from start to run, but the engine should keep running. I would through a spare relay in the glove box, just in case!
Joe
Last edited by Joe H; 03/04/2013 9:23 AM.
