Here's an old post of mine:
If you have a self-serve junkyard in your area, find a GM car with a similar body style and an HEI ignition. Remove the engine wiring harness and unwrap it. You only need the section from the HEI to the firewall so you can cut it out of the car as necessary.
Remove any sealant covering the wires as they enter the firewall plug. Using a very small flat-bladed screwdriver (eyeglass size), insert the blade just under the firewall plug wire for the + side of the ignition. This will release the wire from the firewall plug. Practice on a few of the other wires first so you can get the feel for how they remove. Now you have a splice-free wire to work with. Install this new wire into your orignal points wire location on your firewall plug and reseal the wire with silicone. Once you get the hang of it it will be very easy. You may want to buy the whole harness and use the extra wiring for future accessories since there are extra locations on the firewall connections that you can use, instead of drilling holes, to pass wiring through.
The purple wire triggers the starter. It should go on the small engine side post on the stock GM solenoid.
When converting to HEI you do not need the other small wire that attaches to the solenoid. This wire provides 12v to the coil during startup when a points ignition is used. It is likely that either you have your ignition wire attached to either the purple wire or the small wire and hence that is why the engine only runs in the start position.
Also, you cannot hook up an HEI ignition to any 12v source. It should be hooked up through the original 12v connection on the firewall engine plug for proper operation. If connected in the wrong place you will burn fuses or melt wiring. The wire should also be 12ga minimum.
A GM Factory Assembly Instruction Manual will be a lot of help. It has a basic wiring diagram that will help you locate the proper terminal on the firewall plug.
The Red Beast http://www.geocities.com/casanoc
[This message has been edited by CarlC (edited 06-15-2001).]