Chevelle Tech - View Single Post - Distributor wiring puzzle
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post #1 of (permalink) Old May 29th, 17, 3:25 PM Thread Starter
lucifershammer
Senior Tech Team
Steve
 
Join Date: Sep 2015
Location: Central MA
Posts: 1,531
Distributor wiring puzzle

When I bought my 72 Chevelle, the PO had already converted it to a big block (from a 307) and an HEI ignition. He also had put in a single wire alternator, which I have since fixed and installed a 12si alternator and just did the simple kit to bypass the external regulator (one of the first things I had to fix.). GEN light works now and charges at 14.6 volts (old one wire would only charge at 13.5 or so.)

The car always started and turned off just fine. But, what was bugging me was that the power lead to the HEI was a 16 or 18 gauge wire (tiny) coming out of the taped up harness somewhere.

So, I finally got around to it and installed a relay with 12 gauge power feed and output. Connected the power lines to the horn relay and then the distributor. And decided to use the old tiny power wire from the distributor to trigger the relay on and off.

Here is where it got interesting. Car started up and ran great - I do believe it is running better than before this change. Then I turn the key off, and the car keeps running.

Disconnect the trigger wire (old wire that was powering the HEI) and it shuts off. Pull out the voltmeter and find a few interesting things.

Ignition off - no power to trigger wire.
Ignition on - 12v to trigger wire
Start car, turn ignition off, car keeps running, and 6v to trigger wire. Disconnect relay, car stops, voltage goes to 0 on trigger wire.

Now, obviously 6v won't run an HEI directly, which is why I believe the car always started and shut off fine. But now that I'm using that as a trigger, it is enough to keep the relay tripped and thus the car keeps running.

Any idea where this wire might be coming from? Is it the old resistor wire? Why it would have 6v on it after ignition off?

Easy to fix (just find another START+RUN trigger source) but just wondering if I should keep digging if there could be another underlying problem. I'm assuming some sort of alternator backfeed, not sure if I should hunt it down and solve it or just use a different source for the ignition trigger.

1972 Chevelle, 454, 200-4r non-lockup, 12 bolt 3.73
1981 Camaro Z28, 355, TH350, 3.73
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