[VetteVet]

This is a common problem with the one terminal mini starters. You are only applying power to the coil in the run position from the key switch. The 67 switches are different from other later years as they have no accessory position.

Your two small wires to the starter are the purple 12 gauge and a smaller 16 gauge yellow wire. The purple wire is the starter solenoid wire and the yellow wire is the ignition resistor bypass wire which sends voltage to the OEM coil for starting with a full 12 volts, but only while cranking.

Since the PO has installed the HEI distributor, he has probably disconnected the small yellow wire since the HEI requires a full 12 volts at all times. This is probably the reason you don't have voltage to the distributor during crankiing.

The solution is pretty simple, but first you need to establish where you are powering the HEI from. As was said if it's from the IGN-UNfused terminal on the fuse panel and it has power while cranking you are good. It seems that you are not getting power there while cranking or you are powering the HEI from another source. Possibly the firewall block where the original resistance wire was located which the PO might have eliminated to run the ignition to the HEI.

If you find that the IGN-UNfused terminal has power in the cranking position with the key switch then all you have to do is switch your distributor ignition source wire to that.

You can't just run a jumper wire from the purple cranking wire to the distributor because you would continue to feed the solenoid when the truck starts and the key is returned to the run position. You have to cut the power to the distributor as soon as you release the key to run or the starter would continue to turn.

Here's a couple of easy fixes.
1. Run a wire from the purple wire to the distributor and tap it into the ignition power wire say it's a 12 gauge red or pink wire. This gives you ignition voltage while cranking.
But remember I said that would feed the solenoid in the run position. To prevent that all you need to do is solder in a small diode in the jumper wire and you would get the cranking voltage but the diode would stop the feedback.

2. Install a Bosch relay in the ignition wire and run a wire from a hot source, battery positive to terminal 30 on the relay and run another wire from terminal 87 to the distributor wire feed. Then run a small gauge wire to the relay from the purple wire to terminal 86. Then run a ground wire to terminal 85 on the relay and the relay will send
ignition voltage to the distributor whenever you hit the starter. when you release the key
the ignition voltage will run to the distributor.

Even if you replace the starter you will still have to run the small wire to the distributor.