I have a 65 442 that I want to put an HEI coil/distributor in. There are 2 existing wires to the coil. One is yellow and the other is white and looks like a resistor wire. from everything I read it says I need a full 12 volts on the HEI coil and I'm wondering if the existing coil wires will provide that or do I need to run a separate lead to the coil and abandon the old ones. Right now I am just putting things back together as I pulled the engine and have the dash out so no power to it. Looks like the ignition wiring was replaced with a new harness. I pulled the engine to clean up the engine compartment and I am putting a 200 4r transmission in. Wondering if anyone can answer this - Thanks in advance for the advise.

 

You will need a full 12V, either from the heavy pink wire that comes from the ignition switch, or by removing the lug in the square firewall through-plug that connects to the coil resistor wire and replacing the resistor wire with a copper wire at that point.

- Eric

 

You probably will still need the yellow wire as the coil needs 12v during start cycle, it comes from the starter.

 

The reason for the yellow wire from the starter is because of the resistor wire.

The coil in the older system is designed to run on about 8-9V all the time, but has the capacity to run on 12V for brief periods without overheating, and when running on 12V will produce a higher voltage.

Setting it up to briefly put out a higher voltage while starting gives you surer starts, and makes sure that even with a discharged battery (let's say, 9V while cranking), you will still have enough of a spark to get it started.

HEI puts out a much higher voltage all the time, and so always delivers that hot spark when starting.
Since HEI has to run on 12V, there is no advantage to running the yellow wire from the starter, because it gets the maximum voltage that the system can deliver, from the ignition switch, no matter what, already. If your battery is low and only putting out 9V, you will be getting 9V from either the ignition switch or the starter terminal (or both) - doesn't matter.

It won't hurt to leave the yellow wire connected, but it won't do any good either.

- Eric

 

I like to use the resister wire to run a relay directly wired to the battery bus.

 

Eric, I believe on his car there are 2 seperate circuits, run is supplied by the switch through the resistor wire and start through the solenoid to the distributor. You are correct that the solenoid bypasses the resistor wire to provide the a full 12v to the coil during start.

 

That's right!
Mid-60s cars have that "one or the other" ignition switch where if you leave one wire off, the car will only run while cranking, or will never start while cranking, depending on the wire.

He definitely needs both wires.

Ooops.

- Eric