HEI power supply.

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HEI power supply.

Post by rfoll » Sun Mar 17, 2019 9:34 pm

I'm working with a 64 Malibu with an aftermarket HEI distributor. They used the resistor wire to power it, and it was running ok, but HEI requires a full 12 volts. I found a switched, fused 12 volt supply at the fuse panel, but I'm unsure of how many amps one of these distributors draw. I have been unable to find an un-fused switched 12 volt supply. I don't like the idea of a fused distributor wire, but options are limited without crawling under the dash to look at the ignition switch. I suspect everything there is soldered. Will a 30 amp fuse be reliable? The owner is a woman that needs to be reminded to change oil. Also, they tapped into the wiper supply to power the electric choke on the Edelbrock carb. Any thoughts on this are welcome. This is a very low mile original car and I am loath to start hacking the wiring.
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Re: HEI power supply.

Post by psychomotors » Sun Mar 17, 2019 9:38 pm

On my 69 Chevy pickup , I just found a hot wire in run (I think pink ) coming out of the ignition switch and spliced into it. I drove it for about 5 yrs, sold it to a buddy who drove it 10 or so years. No issues. This was approx. 25 yrs ago , hence the trouble remembering the wire color.
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Re: HEI power supply.

Post by ProPower engines » Sun Mar 17, 2019 9:39 pm

I would tap into the ignition directly to power the choke and the distributor.
That way you will have a full 13.5 volts when running. the choke is the issue so I would fuse that but if you must fuse the ignition I would use at least a 40-50 amp fuse as the HEI coils draw a lot of juice and some coils I have seen draw 20 + amps.
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Re: HEI power supply.

Post by rfoll » Sun Mar 17, 2019 9:48 pm

There is a diagram I have seen that uses the original resistor wire connected to a relay. Maybe that would be my best bet. There is also an adapter that connects up stream of the fuse to bypass it, but I am unsure of the load capacity. I am working on this car for free and i'm not wanting to get real involved in time consuming repairs more than I have to. I am already well into a full rebuild on the engine. It starting to look like popping the switch out of the dash is my best option.
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Re: HEI power supply.

Post by jred » Sun Mar 17, 2019 10:03 pm

down here in Arizona I can't tell you how many guys with HEI have used the factory resistor wire to try and run an HEI good or bad we just run a 10g wire from the run side of the ignition switch to the battery terminal on the HEI as this dist. needs a full 12volts

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Re: HEI power supply.

Post by In-Tech » Sun Mar 17, 2019 11:14 pm

rfoll wrote:
Sun Mar 17, 2019 9:48 pm
There is a diagram I have seen that uses the original resistor wire connected to a relay. Maybe that would be my best bet. There is also an adapter that connects up stream of the fuse to bypass it, but I am unsure of the load capacity. I am working on this car for free and i'm not wanting to get real involved in time consuming repairs more than I have to. I am already well into a full rebuild on the engine. It starting to look like popping the switch out of the dash is my best option.
To me that's the easiest route. I just did a '68 chevelle and mounted a relay on the firewall, done in a few minutes.
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Re: HEI power supply.

Post by MT Jeff » Sun Mar 17, 2019 11:42 pm

If you want to get fancy you could use a relay to power the distributor and choke. Then run the choke through a oil pressure switch so it only gets power when the engine is running. That way if the ignition is on but not started the choke won't open causing a hard start. That's how I would do it.
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Re: HEI power supply.

Post by Schurkey » Mon Mar 18, 2019 12:22 am

MT Jeff wrote:
Sun Mar 17, 2019 11:42 pm
If you want to get fancy you could use a relay to power the distributor and choke. Then run the choke through a oil pressure switch so it only gets power when the engine is running. That way if the ignition is on but not started the choke won't open causing a hard start. That's how I would do it.
Ignition needs to be powered in "Run" and "Crank" positions of the ignition switch.

Choke should have power only in "Run" so that extended cranking doesn't open the choke. Then, just like you said--through the oil pressure switch so that if the engine stalls while the owner is inside having another cup o' coffee while the vehicle warms up, the choke isn't still getting power.

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Re: HEI power supply.

Post by Tuner » Mon Mar 18, 2019 3:01 am

Remove the pink wire (that would otherwise connect to the inner BATT + in the cap) from the 3 wire connector and connect it to the ballast resistor wire from the ignition switch.

Connect the BATT + terminal in the cap directly to the battery + using 10 ga. wire.

This arrangement powers the coil + directly from the battery and switches the module on and off with the key.

Take care if there is a tachometer connected to the COIL - because it is hot all the time through the coil primary, key on or off.

Key On Engine Off, the module senses the engine is not turning and does not ground the coil until the engine cranks or runs. Take care some cheap china modules may not have this safety feature.

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Re: HEI power supply.

Post by Geoff2 » Mon Mar 18, 2019 5:08 am

HEI modules control the coil current & the modules are internally current limited to about 5.5 amps. A 10 amp fuse is the correct size. No way would you want to use a 50 amp fuse. Harness would be smoldering before fuse blew......

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Re: HEI power supply.

Post by Circlotron » Mon Mar 18, 2019 8:24 am

Geoff2 wrote:
Mon Mar 18, 2019 5:08 am
HEI modules control the coil current & the modules are internally current limited to about 5.5 amps. A 10 amp fuse is the correct size.
^^ What he said.

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Re: HEI power supply.

Post by novadude » Mon Mar 18, 2019 8:47 am

On my '65 Nova, I used removed the resistor wire from the firewall plug and replaced with another wire that I used to switch on a relay. The relay pulls the power for the ignition (10g wire to "BATT" terminal) from the horn relay bus. Works fine.

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Re: HEI power supply.

Post by Tuner » Mon Mar 18, 2019 1:07 pm

novadude wrote:
Mon Mar 18, 2019 8:47 am
On my '65 Nova, I used removed the resistor wire from the firewall plug and replaced with another wire that I used to switch on a relay. The relay pulls the power for the ignition (10g wire to "BATT" terminal) from the horn relay bus. Works fine.
Relays like the 30~40 Amp Bosch cubes draw so little Amperage It isn't necessary to eliminate or replace the resistor wire If the resistor wire is only used to switch a relay.

However, if it is powering something else that may need full 12V, such as an electric choke, then replace it with regular wire or power the something else with another relay.

HEI ignitions must always have full battery voltage but If an electric choke is opening too fast it might be desirable to leave the resistor wire or add a resistor in the wire to the choke to slow down the opening rate.

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Re: HEI power supply.

Post by tresi » Tue Mar 19, 2019 2:07 am

The instructions for my MSD HEI module said to a minimum of a 14 gauge wire and the MSD module is said to pull 7.5 amps. I've used this module several times and the stock HEI wiring or I used a 12 ga never a problem.

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Re: HEI power supply.

Post by Schurkey » Tue Mar 19, 2019 4:10 am

tresi wrote:
Tue Mar 19, 2019 2:07 am
the MSD module is said to pull 7.5 amps. I've used this module several times and the stock HEI wiring or I used a 12 ga never a problem.
7.5 amps PEAK, but the amperage draw pulses with each charging of the ignition coil. The average draw will be less than 7.5 amps. Wiring has to be big enough to allow the peak amperage to flow unrestricted. That's why they mandate 14-gauge wire minimum. I thought GM used 12-gauge on their HEI applications.

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