#1  
Old 02-10-2024, 08:07 PM
wooftfd wooftfd is offline
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Default HELP! HEI install and electricial problems

Ok, put in a new motor, 1964 GTO, 1964 421, fresh build, mild motor, HEI, M&H electrical wiring harness...,
Had engine low voltage to coil while running, so installed simple relay with full 12V power, triggered by normal coil + wire. Low voltage backfeed from the dash battery light system kept the relay energized, so car would run after switched off. Next step was to put a IN4002 Diode on the R Alternator wire. Black with White stripe, goes to the 2rd position on voltage regulator. Car starts and stops with ignition switch, but now battery light is on while car is running, Bright, and voltage from Alternator jumps up to 16... only thing I did was install the diode... F wire (2) is blue wire, goes to position 1 on Voltage Regulator, has o volts in key off, 9.7V with key in run position. Diode was to correct "runon" and did.

No electrical issues prior to the diode install... voltage constant, 14.5V, battery light operated as normal... Thoughts???


Last edited by wooftfd; 02-10-2024 at 08:30 PM.
  #2  
Old 02-10-2024, 09:15 PM
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65 Lamnas 65 Lamnas is offline
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I'm putting an HEI in my '65 when I put in my new motor for this summer. I also have an M&H harness,, but ordered it "with HEI"....hopefully 10Ga wire will get the job done without significant voltage drop. I think I'd try to figure out and correct the low ignition voltage issue and forget the rest of it....but that's just me blabbering.

  #3  
Old 02-10-2024, 09:26 PM
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george kujanski george kujanski is offline
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Diode should be in series with the brown wire to terminal 4 of the regulator ( the opposite end from the blue "F" wire terminal. The band end of the diode should point towards the regulator.

George

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Old 02-10-2024, 11:55 PM
wooftfd wooftfd is offline
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Terminal 4? ok, I can do that... It sure seems theres some difference of opinion between folks, but so far, having it in the T2 wire, M&H harness is black with white stripe is not giving me the desired results...
would that be why the battery light is on during the run key position, bright, and the voltage is jumping as high as 16?
everything was ok on the charging side before I added the diode on the T2, R side of the alternator, I was just trying to cure the HEI run on situation...
So after the regulator, before it goes into the firewall connector?

  #5  
Old 02-11-2024, 05:35 AM
Joe's Garage Joe's Garage is offline
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Default George is THE man when it comes to electrical gremlins on this Forum.

If he tells you how to fix an electrical issue, be assured that following his advice will absolutely fix it.

Thanks George!

  #6  
Old 02-11-2024, 12:11 PM
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george kujanski george kujanski is offline
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Anywhere in the brown wire as long as the band end of the diode points to the regulator, not to the firewall.

What happens is when you turn the key on, current goes from the ign. switch thru the brown wire to the regulator then thru the regulator, then to the alt field (blue wire) to excite the alternator. Once the engine starts and the alt produces output, there is a backfeed from the alt to the brown wire to the idiot lite and ignition circuit. Since you have a relay feeding the HEI, the amount of backfeed thru the idiot lite is enuf to keep the relay on. Normally without a relay, the backfeed amount is too small to provide enuf current for the HEI, and the ignition dies.

The diode allows excitation but blocks the backfeed and the idiot lite works normally.

Joe, thanks for your support!

George

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  #7  
Old 02-11-2024, 02:08 PM
wooftfd wooftfd is offline
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Thank you Sir! I'm sorry, I didnt word that last post very well, I just meant that I have been reading forms and watching videos for a week now, and there are so many different directions of what to do... I was surprised with the number of HEI's folks have installed that it wasnt well known knowledge.
I went back and searched other posts Mr. Kujanski made on the topic, and see he is about as good as it gets on the subject!!!!!
Thanks again!!!!!!!!!

  #8  
Old 02-12-2024, 10:39 PM
wooftfd wooftfd is offline
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Just wanted to report I did the re-wiring job today, and she starts, runs, stops, and charges like designed!!!
Thank you George!!!!!!!

  #9  
Old 02-13-2024, 10:41 AM
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Glad it's now working!

George

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  #10  
Old 02-13-2024, 10:41 AM
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FWIW only, when I did the HEI upgrade, I also went to an SI alternator with an internal regulator. MH sells a harness made for that as well. I had read somewhere in this forum that HEI failures in the early cars might be due to the external regulator. That being true or not, it's been very reliable. Also, I went with an NOS GM HEI module & coil.

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Old 02-14-2024, 03:46 PM
wooftfd wooftfd is offline
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Nice! The car I'm working on was restored a while back, and it came with it's original engine and transmission. I've swapped them out, and are saving them, so when I sell it, the new owners can decide if they want to keep it drivable, or totally restored. My goal with the wiring mods was to keep it as stock as possible, and easy to return to "as built" so only changing what I have too...

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