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Old 01-24-2023, 01:23 AM   #1
howzzzit
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To fuse or not to fuse? That is the question.

Installing a hei distributor and using the non fused ignition terminal in the fuse box. Inline fuse or not? If so, amperage of fuse?
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Old 01-24-2023, 01:39 AM   #2
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Re: To fuse or not to fuse? That is the question.

No fuse. Distributors were never fused from the factory HEI or otherwise.
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Old 01-24-2023, 09:52 AM   #3
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Re: To fuse or not to fuse? That is the question.

I converted to HEI sometime in the 1980s. No fuse, never had a problem.
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Old 01-24-2023, 10:17 AM   #4
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Re: To fuse or not to fuse? That is the question.

You need to run an infused non resistor wire that supplies a full 12volts for an HEI
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Old 01-24-2023, 12:23 PM   #5
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Re: To fuse or not to fuse? That is the question.

Infused? I'm not sure what that means.
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Old 01-24-2023, 12:50 PM   #6
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Re: To fuse or not to fuse? That is the question.

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Originally Posted by HO455 View Post
Infused? I'm not sure what that means.
He's referring to a fusible link and the fact when replacing a points distributor you need to remove the resistor wire that cuts voltage to the points. That's the correct way to do it, although MANY are installed without and function correctly.

https://www.onallcylinders.com/2017/...ible-links-go/
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Old 01-24-2023, 12:58 PM   #7
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Re: To fuse or not to fuse? That is the question.

I ran a dedicated wire, 10 gauge, from IGN tab of fuse block to my HEI (pertronix module) dizzy. my IGN fuse is 10amps.
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Old 01-24-2023, 09:48 PM   #8
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Re: To fuse or not to fuse? That is the question.

I think it is easiest to take the power straight from the bulkhead connector like this. https://www.67-72chevytrucks.com/vbo...d.php?t=708975

Fuse is not necessary but if you would like to add one inline anyway it should work fine with a 10 amp fuse. I find my HEI takes 2 amps of current to run.

I suggest now is an opportunity to check that you have a fusible link wire at the battery to protect the smallest gauge unfused wiring in your truck. In a truck wired like stock the unfused wiring before the fuse panel is 12 gauge, so you would use 6 to 9 inches of 16 gauge fusible link wire to connect the 12 gauge red wire to the battery.
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Old 01-24-2023, 11:54 PM   #9
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Thumbs up Re: To fuse or not to fuse? That is the question.

hi, I used the ing. unfused but I put a 10 amp fuse in line. you never know. post 8 is the cleanest way but I find the the way your speaking of is super quick. brown 70
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Old 01-25-2023, 01:14 PM   #10
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Re: To fuse or not to fuse? That is the question.

Using a 10 gauge wire for the HEI IS THE EXACT OPPOSITE of a fusible link. A fusible link is, by design, the weakest link in an electrical circuit. A fusible link is designed to FAIL first and protect the rest of the circuit.

A 10 gauge wire for the HEI becomes the strongest link in the circuit.

The 12 gauge wire from your fuse box to the ignition switch, the ignition switch, the 12G wire from the ign sw to the bulk head connector and the 12g wire to the battery, all become more susceptible to excessive current than your 10 gauge HEI wire.
The truck could burn to the ground and your precious 10 gauge wire would remain unscathed.

The original, factory HEI wire connecting the HEI to the bulkhead connector was 14 gauge wire. This 14 gauge wire had a very unusually extra thick insulation. It might be the extra thick insulation that has led many to believe it is a larger wire.

As dmjlamber pointed out, the factory HEI uses less than 2 Amps. I've measured it. Apparently djmlambert has also.
OK, you don't believe me. Would you believe General Motors.
The image below is from the 1975 Chevy Truck page in the GM Heritage Archive.

Ignition - 2 Amps, The same as the brake lights, Half is much as the Horn. Although these items draw current for short time periods.

A 10 amp fuse will allow the HEI to completely melt, before the fuse blows.
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Old 01-25-2023, 02:52 PM   #11
LockDoc
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Re: To fuse or not to fuse? That is the question.

Quote:
Originally Posted by Orange71shorty View Post
You need to run an infused non resistor wire that supplies a full 12volts for an HEI
Quote:
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Infused? I'm not sure what that means.

I'm pretty sure he meant "unfused" and hit a wrong key. The I and U are right beside each other. I'm bad about doing that with my two fingered typing and CRS....

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Old 01-25-2023, 03:15 PM   #12
Orange71shorty
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Re: To fuse or not to fuse? That is the question.

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Originally Posted by LockDoc View Post
I'm pretty sure he meant "unfused" and hit a wrong key. The I and U are right beside each other. I'm bad about doing that with my two fingered typing and CRS....

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Yes I meant unfused, autocorrect or fat fingers took over lol
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Old 01-25-2023, 05:54 PM   #13
howzzzit
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Re: To fuse or not to fuse? That is the question.

On another note about using the unfused ignition. There is a pink (or faded red) wire on one of the terminals. I can't trace where it goes. Definitely not for the distributor as I am currently running points. Any ideas what is powered with ignition on?

Think I found it. Definitely pink. Traced through the wiring gutter to a loom going down to the solenoid on the Quadrajet. Now the question is should that be on the unfused ignition? I didn't put it there, but someone helped me install a new engine and maybe they put it there? If not where? Since I want to hook up the hei to ignition unfused would it be too much amperage draw for the terminal?

Last edited by howzzzit; 01-25-2023 at 07:31 PM.
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Old 01-25-2023, 08:34 PM   #14
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Re: To fuse or not to fuse? That is the question.

It may be for the electric kickdown switch on the carburator, that sends voltage to a terminal on the TH400 transmission at full throttle.
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Old 01-26-2023, 03:47 AM   #15
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Re: To fuse or not to fuse? That is the question.

Read dmjlambert's link in post #8 above. Connect the HEI wire to the bulkhead connector as shown in that link. That is the most direct route to the 12volts at the ignition switch.
DO NOT connect anything else to the ignition circuit. NOT at the HEI and not anyplace from there up to the ignition switch.
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