Firewall block resistance wire for HEI or use relay

[IT Cowboy]

I am putting in a new HEI dist.with an ext. coil. I found the post about the “step down” resistance wire that is in the wiring block on the firewall and how it can be replaced and ran to the coil as a 12v source. Is that still a good method to wire the coil or would it be better to run it or another ignition on wire through a relay direct from the battery and a fuse.

Maybe I am over thinking it as I have a yellow wire on the current coil but I think it comes from the starter relay and is also connected to the resistance wire mentioned above.

['68OrangeSunshine]

Don't use the 20 Or-Ppl-Wht/20 Yellow wire from the bulkheasd connector for HEI.
That resistance wire heats up during use -- increasing resistance -- so you don't burn up the points.
HEIs require a constant 12 vdc. A variable undervoltage can burn an HEI Coil up.
Run a new 12 gauge line from IGN Unfused on the Fuse block thru the firewall to the +Pos Coil terminal.
I don't have either a relay or fuse.
Yes you could use that terminal on the Bulkhead Connector to run a new line to the HEI Coil. I just ran a separate wire. In theory, I could go back to Points. Not in the near future, though.

Cap off the old Yellow coil wire.

[Willshook]

Originally Posted by '68OrangeSunshine

Run a new 12 gauge line from IGN Unfused on the Fuse block

This.

[IT Cowboy]

Here is the tutorial I found that does away with the resistance wire

https://67-72chevytrucks.com/vboard/...d.php?t=708975

Could I cut that white cloth wire at the bulkhead and connect a new wire to it on the bulkhead side? If I don’t have a new wire and terminal connector to put in the bulkhead

Edit I think I answered my own question as that white wire out of the bulkhead is only 20 ga

[lil hoodlum]

^^^^^^ Yes, to the last 2 posts. I did the same, new 12 gauge wire directly to the IGN unfused and HEI distributor.

[70STOVEBOLT]

Packard 56 male terminals are readily available for 12 gauge wire. Take the bulkhead apart and remove the resistance wire and replace it with the 12 gauge pink wire (OEM color), or color of your choice. This is the best way of doing this, and the cleanest looking (IMO of course).

[IT Cowboy]

Originally Posted by 70STOVEBOLT

Packard 56 male terminals are readily available for 12 gauge wire. Take the bulkhead apart and remove the resistance wire and replace it with the 12 gauge pink wire (OEM color), or color of your choice. This is the best way of doing this, and the cleanest looking (IMO of course).

I glanced at this and thought what does a 56 Packard have to do with any of this.

[IT Cowboy]

And the firewall bulkhead connection will probably be the winner on what to go with here.

[54blackhornet]

Do yourself a big favor and look up MAD Electrical. You will find all the knowledge you need to upgrade your electrical system. HEI ignition was introduced back in 1975. It’s a very simple upgrade ONCE you become familiar with the basics. You don’t need to disassemble the junction block. No relays are necessary.

[A1971Blazer]

Not sure what your budget is, but for around $100 you can get an engine harness specifically for HEI. As a bonus, all the other engine-specific wires will be brand new.
The wiring on one of my trucks was hacked up badly. It was easier to just replace the entire engine harness.

[IT Cowboy]

Originally Posted by A1971Blazer

Not sure what your budget is, but for around $100 you can get an engine harness specifically for HEI. As a bonus, all the other engine-specific wires will be brand new.
The wiring on one of my trucks was hacked up badly. It was easier to just replace the entire engine harness.

More info please, from where or who and how was the install. I have heard bad comments about Painless kits

I installed the headlight relay wiring kit a few weeks ago to where it uses the headlight switch to trigger the relay instead of running the juice through the headlight switch.

[A1971Blazer]

Originally Posted by IT Cowboy

More info please, from where or who and how was the install. I have heard bad comments about Painless kits

I installed the headlight relay wiring kit a few weeks ago to where it uses the headlight switch to trigger the relay instead of running the juice through the headlight switch.

Here's the link to M&H, but the price has gone to $200 since I bought mine several years ago!

https://www.wiringharness.com/part-n...id=&orderable=

['68OrangeSunshine]

M&H is my choice, too. If you need a new harness. Made in USA by Americans. The electrician puts his name on the harness.
They use Factory color codes, wire gauges, and exactly correct terminals.
Closest you can get to a fresh Factory loom.
But not cheap.

[Classics Fan]

Originally Posted by '68OrangeSunshine

…HEIs require a constant 12 vdc. A variable undervoltage can burn an HEI Coil up.
Run a new 12 gauge line from IGN Unfused on the Fuse block thru the firewall to the +Pos Coil terminal.
I don't have either a relay or fuse…

This is how my HEI was powered when I bought my 71 Jimmy in 2018. Previously I had a 68 Pontiac LeMans with HEI wired the same way. On both vehicles I installed an inline 20A fuse. How and why is one not necessary? Relying on the fusible link to protect that wire?

[Rick Bollinger]

ITCowboyIf you installed the headlight relay kit then you could go with a relay for the HEI as well. Use the 20 ga wire from the harness for the trip wire on the relay. You remove so many amps going through the main harness at the fuse box. Leaving more power for a modern stereo or a small amp etc. Hei with a upgraded coil can draw upwards of thirty amps. Taxing the original harness. Yes replace the resistance wire with a 20 ga wire.

[dmjlambert]

Sorry but I'm not a fan of that idea. No relay needed, it only draws 2 amps unless something has gone terribly wrong, and the simpler you make the wiring the fewer things there will be to burn out or break. Just remove the resistance wire by squeezing the male terminal in the connector block and pushing it out the back as shown in the tutorial. Replace with a new 12-gauge pink wire with new terminals, and make sure you use an HEI connector on the distributor so it will have the little plastic tab that holds the connector in place. You can remove the engine harness if you're feeling energetic, unwrap it and remove the cloth covered white wire with its yellow wires to the old coil and starter, and stash it or sell it in the parts section for people going back to points, and re-wrap the wiring harness with new non-adhesive black vinyl tape.

[Rick Bollinger]

dmjlambert I was off a little. It says upward of 8 amps depending on which unit and coil, distributor you go with. I did exactly what you are saying and ran it till I took my truck apart with no issues. Now I run relays for headlights, Fitech, sub wolfer, trailer brakes and hei. This leaves more available amperage for radio, slide bar custom autosound which takes a constant hot plus a switched hot. and other little upgrades like cell phone charger ect.

['68OrangeSunshine]

Originally Posted by Classics Fan

This is how my HEI was powered when I bought my 71 Jimmy in 2018. Previously I had a 68 Pontiac LeMans with HEI wired the same way. On both vehicles I installed an inline 20A fuse. How and why is one not necessary? Relying on the fusible link to protect that wire?

Well, if running an inline 20@ fuse on your HEI 12 Volt feeder helps you sleep at night, good for you.
I've never had a problem on either of the two trucks I've upgraded to HEI. '71 GMC Jimmy, w/350 V8 and a '68 C/10 Stepside w/292 L6.
Occasionally an Ignition Module blows out, but I don't think that's a related issue. But good idea to always keep a spare Module [and white heatsink stuff] in your glovebox.

[tim_mc]

Originally Posted by '68OrangeSunshine

Occasionally an Ignition Module blows out, but I don't think that's a related issue. But good idea to always keep a spare Module [and white heatsink stuuf] in your glovebox.

Thanks for the reminder. I have a spare OE module in the glovebox, but need to include a packet of heatsink paste.

Also, not to be a broken record - not all HEI modules are the same. I road tested an OE module and a Davis Unified Ignition (Performance Distributors) Dyna-Module back to back, and wow, what a difference. Stock module just dogged it while the DUI module has much better throttle response. No contest.

['68OrangeSunshine]

Originally Posted by tim_mc

Thanks for the reminder. I have a spare OE module in the glovebox, but need to include a packet of heatsink paste.

Also, not to be a broken record - not all HEI modules are the same. I road tested an OE module and a Davis Unified Ignition (Performance Distributors) Dyna-Module back to back, and wow, what a difference. Stock module just dogged it while the DUI module has much better throttle response. No contest.

Where are the Davis modules sold? Proprietary part?
I had a glovebox module fail on my '68 C/10 L6 292 at the supermarket parking lot this February. Truck wouldn't start to go home. Ran fine the 3 miles there. Popped open the hood, went into the Distributor cap, and found my Rotor was loose and cockeyed. [!?] Screwed the Rotor on right. No go. Tried my backup module. It fired right up, then died. Timing seemed weird. Wouldn't stay lit on successive tries. Had to call a Hook. That Module was used but had tested good. [It may have waited in the glovebox for 2 years or more.] Now O'Reilly's told me they can't test them anymore. AutoZone tested it and said it was BO. Got a replacement under warranty there. Got a warrantied Rotor at ORAP. Had to buy a fresh cap.
Once I bumped the crank, and hand turned it over to TDC and 0 on the timing tab -- Rotor pointing to #1 terminal in cap, I put the fresh components in and it ran fine.
I intended to buy a couple spare Modules from RockAuto. I didn't know there were different grades. It seemed like it was the same P/N for both L6 and V8.

[IT Cowboy]

Originally Posted by '68OrangeSunshine

Where are the Davis modules sold? Proprietary part?
I had a glovebox module fail on my '68 C/10 L6 292 at the supermarket parking lot this February. Truck wouldn't start to go home. Ran fine the 3 miles there. Popped open the hood, went into the Distributor cap, and found my Rotor was loose and cockeyed. [!?] Screwed the Rotor on right. No go. Tried my backup module. It fired right up, then died. Timing seemed weird. Wouldn't stay lit on successive tries. Had to call a Hook. That Module was used but had tested good. [It may have waited in the glovebox for 2 years or more.] Now O'Reilly's told me they can't test them anymore. AutoZone tested it and said it was BO. Got a replacement under warranty there. Got a warrantied Rotor at ORAP. Had to buy a fresh cap.
Once I bumped the crank, and hand turned it over to TDC and 0 on the timing tab -- Rotor pointing to #1 terminal in cap, I put the fresh components in and it ran fine.
I intended to buy a couple spare Modules from RockAuto. I didn't know there were different grades. It seemed like it was the same P/N for both L6 and V8.

I think this is the one listed at Summit Racing but unsure.

https://www.summitracing.com/parts/d...22?seid=srese1

[tim_mc]

Yeah, I've had a few cheapo auto part store modules pop or act weird. I got my DUI module from Summit, P/N DUI-000222:
https://www.summitracing.com/search/...ord=DUI-000222

Read The Reviews. And they're still made in the USA. (Edit: I've had my Dyna-Mod HEI module since 5/31/2021 with no issues. Same P/N for 4, 6 & 8 cylinder GM HEIs: https://performancedistributors.com/...-distributors/.) I also added a hotter 50Kv coil from DUI, which was a replacement for a failed GM/Delco HEI coil after 12 months, so decided to try their module with the upgraded coil. Very glad I did.)

I loved it so much I bought one for my brother's '69 Chevelle SS 396. It really woke it up too. (OK, it was originally a spare for my truck, but don't tell him.)

~Tim

['68OrangeSunshine]

AutoZone's retail price for my new module was in the $70s. I was glad not to pay that. I did think it was inflated.