Distributor wiring puzzle - Chevelle Tech
Electrical & Wiring Troubleshooting electrical problems.

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post #1 of 18 (permalink) Old May 29th, 17, 3:25 PM Thread Starter
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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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post #2 of 18 (permalink) Old May 29th, 17, 3:33 PM
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Re: Distributor wiring puzzle

I suspect that it might be coming through the "GEN" light bulb. Try turning on the radio or heater blower and see if it shuts off then. The load of a radio or blower motor could be enough to drop that voltage and allow the relay to open. Years ago I built a home-made CD ignition for my car and got the same result as you have. Turning on the radio was enough to suck up the extra power going to the ignition.
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post #3 of 18 (permalink) Old May 29th, 17, 4:42 PM
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Re: Distributor wiring puzzle

For HEI just run a 12 gauge from the IGN terminal in the fuse box to the BAT terminal on the distributor. It's that simple, done.

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post #4 of 18 (permalink) Old May 29th, 17, 8:20 PM
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Re: Distributor wiring puzzle

T_R is dead on target, relays are just not worth the effort. IGN< 12 gauge wire from that to the BATT terminal on the HEI, done, finished, simple, easy, works, no relay to fail.

Simple way to do the 12SI is to bridge the BATT term on the back of the alternator, to the number 2 side terminal. If you don't have a charge light, you are finished, works the way it should.

Now, for the charge light, from that old regulator connector, find the number 4 wire, the brown one, and run it to the number 1 terminal on the side of the 12SI alternator, charge light should work as stock, charge rate would be 14.60 volts. All that mumbo-jumbo bridging at the old remote regulator connector is just not needed.
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post #5 of 18 (permalink) Old May 29th, 17, 8:49 PM Thread Starter
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Re: Distributor wiring puzzle

So, the alternator wiring is all already done and has been for 1.5 years now. It was a simple kit I purchased for $10, that you pulled the external regulator, and plugged a connector onto the harness where it was and that did the bridging for you. Then all I had to do was install the 12si internally regulated alternator, plug it in with the other adapter (from the || to the - - connector on the alternator), and viola - everything is working just fine. GEN light and all, charges great, etc.

As I mentioned, the only issue I had today was that I discovered the wire that is powering the HEI BATT terminal was getting 6 volts when the car ignition is switched off after the car is running, instead of going to 0. It wasn't a problem before, but now that I have decided to fix the 16 or 18 gauge wire that was powering the HEI with a relay, I discovered the problem.

I get the idea of running right off the IGN port on the fuse box. I also understand that all the load then goes through the junction block, through the turn signal fuse, and then back out that wire, and thus it is sharing that same power source and draw. I plan to use the IGN to run the HEI, either direct or to trigger my relay.

But, the relay is really not my issue - my original question is still standing - any thoughts on what wire it is that is being backfed 6v after I shut the ignition off, and should I be worried about it? And why 6v? (I'm not really worried about it, and will most likely happily just tuck it away safely in the harness and forget about it, but should I be worried about it? )

1972 Chevelle, 454, 200-4r non-lockup, 12 bolt 3.73
1981 Camaro Z28, 355, TH350, 3.73
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post #6 of 18 (permalink) Old May 29th, 17, 10:25 PM
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Re: Distributor wiring puzzle

I agree with the others, You just need one 12 Vt. wire, Nothing else. This is how I ran my H.E.I. wire. From the fuse panel, Then across the dash, LOOK just above your H.E.I., You will see a plastic plug ( This plug holds the interior insulation to the firewall inside the car).
What I did was cut the tip off of the plastic plug and then ran my hot wire through the center of the plastic plug to the H.E.I.
Bottom line is, Your 12 Vt. hot wire is running through an insulated plastic plug and comes out of the firewall just a few inches from your H.E.I. It is just one less wire that shows up under the hood.
I also hid a toggle switch under the dash so,,,,,,,, If you are playing with some wiring, Or want to bump the engine over, Or doing something that you need the key in the RUN position. Just shut the toggle switch OFF, Now the H.E.I. has no power, With the toggle in the off position , EVERYTHING in the car works,,, BUT you have NO power to the Dist, You can crank it untill the Batt. is dead. Its a kill switch for the dist.
Many ways to wire up an H.E.I.,, Do what is best for you, Its your car.
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post #7 of 18 (permalink) Old May 30th, 17, 6:20 AM Thread Starter
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Re: Distributor wiring puzzle

Thanks. Again. I know how to wire up an HEI.

But, y'all keep missing (or at least not answering) my question, which is not about how to wire up an HEI. That was just back story about how I got to finding the issue I'm asking about.

My issue/question is about the line that is getting a 6v backfeed, why it might be occurring, and if I should worry about it. Ignore the HEI part...

Quote:
Originally Posted by Robinls5 View Post
I agree with the others, You just need one 12 Vt. wire, Nothing else. This is how I ran my H.E.I. wire. From the fuse panel, Then across the dash, LOOK just above your H.E.I., You will see a plastic plug ( This plug holds the interior insulation to the firewall inside the car).
What I did was cut the tip off of the plastic plug and then ran my hot wire through the center of the plastic plug to the H.E.I.
Bottom line is, Your 12 Vt. hot wire is running through an insulated plastic plug and comes out of the firewall just a few inches from your H.E.I. It is just one less wire that shows up under the hood.
I also hid a toggle switch under the dash so,,,,,,,, If you are playing with some wiring, Or want to bump the engine over, Or doing something that you need the key in the RUN position. Just shut the toggle switch OFF, Now the H.E.I. has no power, With the toggle in the off position , EVERYTHING in the car works,,, BUT you have NO power to the Dist, You can crank it untill the Batt. is dead. Its a kill switch for the dist.
Many ways to wire up an H.E.I.,, Do what is best for you, Its your car.
Bob

1972 Chevelle, 454, 200-4r non-lockup, 12 bolt 3.73
1981 Camaro Z28, 355, TH350, 3.73
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post #8 of 18 (permalink) Old May 30th, 17, 12:00 PM
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Re: Distributor wiring puzzle

Please revisit post #2
I stated that your backfeed is likely coming through the GEN light bulb.
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post #9 of 18 (permalink) Old May 30th, 17, 12:33 PM Thread Starter
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Re: Distributor wiring puzzle

Yup, saw that, I thought I had acknowledged that in a separate post, but I see that it didn't get posted for some reason.

Thanks for that - I'll be testing that next, as I suspect you are most likely correct.

BTW - why 6v is a big part of my question too - voltage drop maybe?

EDIT - I just realized this myself after applying a few more brain cells to it - if it is the GEN light doing the backfeeding, it's the resistive circuit in reverse, which would explain why the voltage drops as it is feeding the current back through.

Quote:
Originally Posted by JWagner View Post
Please revisit post #2
I stated that your backfeed is likely coming through the GEN light bulb.

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

Last edited by lucifershammer; May 30th, 17 at 12:52 PM.
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post #10 of 18 (permalink) Old May 30th, 17, 1:56 PM
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Re: Distributor wiring puzzle

Quote:
Originally Posted by lucifershammer View Post

BTW - why 6v is a big part of my question too - voltage drop maybe?

EDIT - I just realized this myself after applying a few more brain cells to it - if it is the GEN light doing the backfeeding, it's the resistive circuit in reverse, which would explain why the voltage drops as it is feeding the current back through.
And the 6v was not enough to power the HEI, which is why the car shut off, but is enough to trip the relay, which is why the car stayed running with the relay.
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post #11 of 18 (permalink) Old May 30th, 17, 3:59 PM
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Re: Distributor wiring puzzle

Well, the IGN terminal is not fused, doesn't run off any fuse, it is direct through the ignition switch.

As far as the alternator, and 6 volts, I've never seen a better way to do a 3 wire 12SI alternator than the way GM did it, large battery cable between BATT on alt, to starter solenoid BATT terminal, jumper wire between alt BATT and number 2, charge wire (brown) off the old remote regulator plug, to number 1, never failed me yet.

I've even used that wiring setup on non-GM vehicles, and even a couple of my friend's fork lifts, and never had problems with it.

Only reason I have ever seen for 6 volt feedback is, one or more of the diodes in the rectifier have issues, or have completely failed in moving voltage only ONE direction. to review, diodes take alternating current and pull one of the poles of volts out to run as DC output. they take the alternating and make it direct.
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post #12 of 18 (permalink) Old May 30th, 17, 4:29 PM Thread Starter
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Re: Distributor wiring puzzle

Quote:
Originally Posted by Dave Ray View Post
Well, the IGN terminal is not fused, doesn't run off any fuse, it is direct through the ignition switch.
Don't want to start an argument here, so that is definitely not my intention, but ...

Everything I have seen so far says it is connected to the turn signals fuse. In fact, I believe (again based on everything I've read, but disclaimer - I haven't empirically tested myself yet, and don't feel like breaking fuses just to pull them all out to try) all 4 of the extra terminals in the fuse box (IGN, BATT, ACC, LPS) are all fused from one of the fuses right next to/near the terminal in question.

As far as I've been able to gather, IGN is fuse protected by the turn signals/heater fuse, ACC is fuse protected by the radio fuse, LPS is fused protected by the instrument lamps fuse, and BATT is fuse protected by the clock/courtesy fuse.

1972 Chevelle, 454, 200-4r non-lockup, 12 bolt 3.73
1981 Camaro Z28, 355, TH350, 3.73
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post #13 of 18 (permalink) Old May 30th, 17, 5:05 PM
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Re: Distributor wiring puzzle

I had the same problem. If I pulled gen bulb, it resolved the issue. I ended up getting a alternator connector that had a diode on one of the leads. This resolved the issue
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post #14 of 18 (permalink) Old May 30th, 17, 6:44 PM
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Re: Distributor wiring puzzle

Quote:
Originally Posted by Dave Ray View Post
Well, the IGN terminal is not fused, doesn't run off any fuse, it is direct through the ignition switch.
The IGN terminal in the fuse box is fused through the BR ALM/ BACKUP 10A fuse adjacent to the IGN spade terminals.


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post #15 of 18 (permalink) Old May 30th, 17, 7:04 PM
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Re: Distributor wiring puzzle

Quote:
Originally Posted by lucifershammer View Post
Don't want to start an argument here, so that is definitely not my intention, but ...

Everything I have seen so far says it is connected to the turn signals fuse. In fact, I believe (again based on everything I've read, but disclaimer - I haven't empirically tested myself yet, and don't feel like breaking fuses just to pull them all out to try) all 4 of the extra terminals in the fuse box (IGN, BATT, ACC, LPS) are all fused from one of the fuses right next to/near the terminal in question.

As far as I've been able to gather, IGN is fuse protected by the turn signals/heater fuse, ACC is fuse protected by the radio fuse, LPS is fused protected by the instrument lamps fuse, and BATT is fuse protected by the clock/courtesy fuse.


For others, read my response (post #14) here:

https://www.chevelles.com/forums/27-e...tched-12v.html
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