12V To Coil From Gear Reduction Starter?

[trymes]

Many years ago, the starter died on my '72 C20 and I had someone install a gear-reduction starter in place of the old original style. I have regretted it ever since, as the sound is just all wrong.

While troubleshooting some other running problems (bad carb rebuild from local shop), I noticed that the new starter doesn't have an R terminal, and the mechanic just left the wire hanging there. This isn't ideal, as it has +9V present when the truck is running, but it wasn't a big issue before, as I was running a Pertronix, but that unit died and I have gone back to points and I want +12V at the coil when cranking.

What is the easiest method to resolve this, such that the coil receives +12V when cranking and then ~9V while running? It currently receives ~9V all the time.

Tom

PS: I have no current intention of swapping to electronic ignition or HEI.

[trymes]

Hmmm....I may have answered my own question with some additional sleuthing:

1. Use a relay to provide +12V to the coil when the key sends +12V to the starter.
2. Wire a Diode inline with the "motor" terminal on the starter. Voltage is only present when cranking, and the diode prevents the ~9V from the coil from energizing the starter (or trying to, at least).

The second one is simpler, and there is a product out there if you don't want to wire it up yourself: https://www.jegs.com/i/JEGS/555/10038/10002/-1

[MARKDTN]

Not a big fan of diodes. It will work as you describe, but I would use a relay instead. If you used a "Bosch" relay it would be 85 to ground, 86 to the "S" terminal (purple wire), 30 to the main starter lug (I'd add a fuse here), and 87 to the coil "+"(yellow wire).