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post #1 of (permalink) Old 07-04-2003, 12:29 AM
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72\' GMC to HEI distributor

I want to ditch the points on my 72' and install HEI. I have a distributor and a connector ready to be wired in for the HEI cap. My question is what does that plug in that comes from the "control modual" go to or connect to? That is the only thing that is stopping it from going in. I cannot find anything in the repair manual I have, and the People at the parts store don't know. I am at a loss and for now have a useless distributor waiting to be installed.
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post #2 of (permalink) Old 07-04-2003, 03:42 PM
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Re: 72\' GMC to HEI distributor

I've done the Points to HEI conversion a couple times. There are a couple things to keep in mind. GMC used a resistor wire from the ignition switch to "+" coil wire connector of the old points coil. The resistor wire knocks down the battery voltage from the ignition switch to the "+" coil wire connector of the old points coil to about 9 or so volts. I strongly recommend running a new wire from the ignition switch to the "BAT" connector of the HEI connector. If the HEI "BAT" does not get full battery voltage when the ignition switch is in the "ON" & "Start" positions the HEI distributor might not work, or if the HEI does work, it's not going to be working very well.

What I usually do, is find the wire on the ignition switch that is hot when the ignition switch is in the "ON" & "START" positions, and splice a new wire to the HEI "BAT" terminal. I usually get a factory HEI "BAT" wire from a junkyard vehicle, that way my installation looks factory. I then remove the "R" wire from the starter solenoid and wrap the connector with several layers of electrical tape and stuff the tapped connector into the wiring harness making double damn sure that the old "R" connector will never ever touch metal.
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post #3 of (permalink) Old 07-04-2003, 03:54 PM
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Re: 72\' GMC to HEI distributor

Thanks, I did not realize that GMC used a resistor wire and not a ballast resistor for the ignition in "Standard" ignition vehicles. I still need to know what to do with the plug in that comes from the HEI's control modual. That is what I need to know right now to make it work.
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post #4 of (permalink) Old 07-04-2003, 09:34 PM
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Re: 72\' GMC to HEI distributor

The plug that comes from the ignition module will plug into the HEI coil / cap assembly. I'm thinking the plug your describing will be a three wire connector. There are a couple different ignition modules used by GM, but I've been thinking your HEI distributor has a 4 pin ignition module. If you have a 5 pin or 7 pin ignition module let me know.
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post #5 of (permalink) Old 07-04-2003, 09:34 PM
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Re: 72\' GMC to HEI distributor

I have got an HEI in my 81 Jimmy and I am sick of it. I really don't like it. I would get an MSD that allows the use of an external coil. Maybe even a Crane system.

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post #6 of (permalink) Old 07-05-2003, 01:03 AM
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Re: 72\' GMC to HEI distributor

The plug coming from the igntion modual is a three hole plug. However, it cannot plug in to my distributor cap because it has four terminals in a square shape

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_ _ Like so. The plug in for the modual is a [000] plug. I just talked to my freind today and he doesn't think that he has the modual plug for his 76'. He is not quite sure though.
Do I really need to use this plug, because it looks like it is unnecassary, but they usually don't put stuff on distributors that is not needed.
I have no idea of what year of truck my HEI distributor came from. I do have the numbers on the side but do they tell you the year of the vehicle it came from?
post #7 of (permalink) Old 07-05-2003, 02:13 AM
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Re: 72\' GMC to HEI distributor

Going by what you describe, you have an Electronic Spark Control (ESC) distributor. The ESC distributor used a 5 pin ignition module. The ESC distributor had two plugs coming out of the distributor, one plug going to the cap / coil assembly, and the other plug went to the spark timing controller. [img]images/graemlins/AR15firing.gif[/img] Get rid of the ESC distributor, it needs a spark timing controller to work.
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post #8 of (permalink) Old 07-05-2003, 01:00 PM
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Re: 72\' GMC to HEI distributor

What year of truck would I need a distributor from then?
post #9 of (permalink) Old 07-05-2003, 03:03 PM
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Re: 72\' GMC to HEI distributor

It doesn't have to be a truck, car will do.
Find one with a vacuum advance on it - they are all over the place for cheap.
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post #10 of (permalink) Old 07-05-2003, 03:20 PM
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Re: 72\' GMC to HEI distributor

The year I describe to get a HEI distributor from would be 1979. In 1981 GM cars started using computer controls on the distributor and carburetor, and the pickups were soon to follow a year or two later depending if the pickup was 1/2 ton, 3/4 ton, or 1 ton. It also depends if the GM vehicle (pickup or car) is a California emission or the 49 state Federal emission package. Usually 1980 vehicles are safe from using computer controlled distributors and carburetors, but it's never fun to find a late 1980 model with 1981 emission packages and the like.
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