To fuse or not to fuse? That is the question. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

howzzzit · 01-24-2023, 01:23 AM

Installing a hei distributor and using the non fused ignition terminal in the fuse box. Inline fuse or not? If so, amperage of fuse?

**67 twins** · 01-24-2023, 01:39 AM

No fuse. Distributors were never fused from the factory HEI or otherwise.

**Stocker** · 01-24-2023, 09:52 AM

I converted to HEI sometime in the 1980s. No fuse, never had a problem.

**Orange71shorty** · 01-24-2023, 10:17 AM

You need to run an infused non resistor wire that supplies a full 12volts for an HEI

**HO455** · 01-24-2023, 12:23 PM

Infused? I'm not sure what that means.

**biketopia** · 01-24-2023, 12:50 PM

Quote:

Originally Posted by HO455

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/

72SB · 01-24-2023, 12:58 PM

I ran a dedicated wire, 10 gauge, from IGN tab of fuse block to my HEI (pertronix module) dizzy. my IGN fuse is 10amps.

**dmjlambert** · 01-24-2023, 09:48 PM

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.

BROWN 70 · 01-24-2023, 11:54 PM

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

RichardJ · 01-25-2023, 01:14 PM

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.

**LockDoc** · 01-25-2023, 02:52 PM

Quote:

Originally Posted by Orange71shorty

You need to run an infused non resistor wire that supplies a full 12volts for an HEI

Quote:

Originally Posted by HO455

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....

LockDoc
.

**Orange71shorty** · 01-25-2023, 03:15 PM

Quote:

Originally Posted by LockDoc

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....

LockDoc
.

Yes I meant unfused, autocorrect or fat fingers took over lol

howzzzit · 01-25-2023, 05:54 PM

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?

**dmjlambert** · 01-25-2023, 08:34 PM

It may be for the electric kickdown switch on the carburator, that sends voltage to a terminal on the TH400 transmission at full throttle.

RichardJ · 01-26-2023, 03:47 AM

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.

01-24-2023, 01:23 AM	#1
howzzzit Registered User Join Date: Dec 2005 Location: Kalifornia Posts: 307	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?

01-24-2023, 01:39 AM	#2
67 twins Senior Member Join Date: Mar 2019 Location: Herculaneum MO (20 minutes south of St. Louis Posts: 582	Re: To fuse or not to fuse? That is the question. No fuse. Distributors were never fused from the factory HEI or otherwise. __________________ 67 C10 283 T5 swapped longbed fleetside = wife's daily driver 67 C20 292 (originally a 250)4speed longbed fleetside w/original wooden bed=my project truck 67 C10 283+.060 (so a 292 as well)T5 swapped longbed fleetside=my DD 72 C1500 Sierra Grande 350 TH350 longbed fleetside=wife's fair weather truck Can you tell we are fans of longbed fleetsides & 67s Chris

01-24-2023, 09:52 AM	#3
Stocker 20' Daredevil (Ret) Join Date: May 2003 Location: Jefferson State Posts: 13,495	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. __________________ - Mike - 1972 K20 LWB 350/350/205 RIP El Jay

01-24-2023, 10:17 AM	#4
Orange71shorty Senior Member Join Date: Feb 2009 Location: Helena, Montana Posts: 528	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

01-24-2023, 12:23 PM	#5
HO455 Post Whore Join Date: Feb 2016 Location: Portland Oregon Posts: 10,787	Re: To fuse or not to fuse? That is the question. Infused? I'm not sure what that means. __________________ Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban the WMB,1991 S(stink)-10 Blazer,1969 GTO, 1970 Javelin, 1952 F2 Ford 4X4, 29 Model A, 72 Firebird. 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377

01-24-2023, 12:58 PM	#7
72SB Registered User Join Date: Apr 2022 Location: Moorpark, CA Posts: 696	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.

01-24-2023, 09:48 PM	#8
dmjlambert Senior Member Join Date: Apr 2016 Location: Cypress, TX Posts: 3,561	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.

01-24-2023, 11:54 PM	#9
BROWN 70 Registered User Join Date: Aug 2010 Location: central oregon Posts: 145	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

01-25-2023, 01:14 PM	#10
RichardJ Registered User Join Date: Apr 2010 Location: So Cal Posts: 1,409	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. Attached Images __________________ '67 GMC 2500, 292, 4spd, AC Last edited by RichardJ; 01-25-2023 at 02:40 PM.

01-25-2023, 05:54 PM	#13
howzzzit Registered User Join Date: Dec 2005 Location: Kalifornia Posts: 307	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.

01-25-2023, 08:34 PM	#14
dmjlambert Senior Member Join Date: Apr 2016 Location: Cypress, TX Posts: 3,561	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.

01-26-2023, 03:47 AM	#15
RichardJ Registered User Join Date: Apr 2010 Location: So Cal Posts: 1,409	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. __________________ '67 GMC 2500, 292, 4spd, AC



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