Sounds like a resistor wire from the ignition switch. They were used in point type setups to kick the voltage back to 8-9 volts. The HEI needs 12 volts.

Try the wire direct from battery positive terminal to dist. Bet it'll run like a charm.

If it does, just replace the wire from the ignition switch to the HEI. Good Luck

Oh, you will have to pull the wire off the battery to shut the car off when you run the hot lead.