Help clarify harness adaptation existing HEI to OE points
 

I’m looking to revert back to the original points distributor in my 72 Blazer. The engine harness is an American Autowire example made for use with an HEI distributor. Am thinking the hot wire to the distributor will require modification with use of a connector that jives with the OE type threaded post on the external coil.

Am I thinking correctly? If so, is there an adaptive connector by chance that I can screw into place on the external coil and plug the existing HEI connector on to without modifying the harness at all?

Here’s what AAW claims:

“This harness is modified for a 12 volt HEI ignition. We replace the original resistor wire with a standard 12 volt feed, and will include a connector for a GM large cap distributor. If you are not using a GM large cap HEI distributor, the connector end may need to be replaced to connect to your system.”

Thanks.

Re: Help clarify harness adaptation existing HEI to OE points
 

You should remove the HEI wire from the harness, and add a resistor wire that goes part way to the engine, and resumes in 2 yellow wires that go to the starter R terminal and the coil. You would probably be able to get that wire from another member by posting a want-to-buy ad in the parts section, or dig it out of your stash if you have the original harness. Harnesses can be unwrapped and re-wrapped because they usually have non-adhesive vinyl tape.

This is the wire you would be putting in. The junction shown by the dot is inside the wire harness before it gets to the end of the wrap that attaches to the engine at the transmission bell housing wire clamp.
https://67-72chevytrucks.com/vboard/...1&d=1465078686

It is the white cloth-covered resistor wire that you would use to replace the wire at your firewall plug, you may have a pink wire there now.

https://67-72chevytrucks.com/vboard/...1&d=1465078686

Squeeze the terminal like this to release it from the connector.
https://67-72chevytrucks.com/vboard/...1&d=1465079038

You'd be doing the opposite of this job, where if you had an orginal harness replacing a points distributor resistor wire with an HEI wire.
https://67-72chevytrucks.com/vboard/...d.php?t=708975

Re: Help clarify harness adaptation existing HEI to OE points
 

Here is one thread that has a diagram.

Link: https://67-72chevytrucks.com/vboard/....php?p=9061422

Hope this helps.

Re: Help clarify harness adaptation existing HEI to OE points
 

The alternative is you can cut your HEI power supply wire, and install a ballast resistor which you would mount on the firewall, change the terminal on the end to the ring terminal to fit on the coil, and run another wire with ring terminals on both ends to the coil and the R terminal on the starter. The ballast resistor or resistor wire reduce the voltage at the coil to preserve the coil and your points. The additional wire going to the R terminal on the starter is to bypass the resistor and provide full voltage to the coil only during start, to give a bigger spark during start.

Re: Help clarify harness adaptation existing HEI to OE points
 

Guys thanks a ton for the replies. I’ll contact AAW and see if they have a schematic of their HEI engine harness.

Was hoping it would be more straightforward like a cut-then-crimp on OE coil connector to the existing harness HEI end. Sounds like doing so would result in electrical failure. Stupid me, I assumed the harness were the same except for something like a packard style connector at the HEI rather than a ring or C clamp connector for an external coil.

I’ve got spare OE harnesses that I can poach from at least. Tempted

Re: Help clarify harness adaptation existing HEI to OE points
 

I don't think it would be all that bad. This is the HEI diagram you would be converting from. Here the wire is pink, not sure what color AAW would have picked.
https://i.imgur.com/n4ZGNrw.png

Re: Help clarify harness adaptation existing HEI to OE points
 

There are several ways to do what you want depending on how factory you want the truck to look.

Replace the HEI harness with a points harness. This would be the factory correct style.

Or disconnect the HEI power from the firewall connector and add a new ballast wire to the existing harness. If you remove the HEI wire and re-wrap the new ballast wire with the correct harness wrap tape it would be the correct factory style.

Or add a ballast resistor to the end of the existing HEI power wire and run a new wire from the other connection on the resistor to your new coil. Mounting the resistor on the coil is a convenient way to do this. See photo. The ballast resistor in the photo has the flat terminal adapter that should allow your current HEI wire to hook right up.

Or leave the underhood wiring as it is and put the ballast resistor under the dash splicing the resistor into the ignition power wire from the ignition switch.

Re: Help clarify harness adaptation existing HEI to OE points
 

Or you could replace the coil with an IC14SB coil from napa. It does not need an external resister.
That would be the way I would do it , I dislike the porcelain resisters as they are prone to be a problem down the road.

David

Re: Help clarify harness adaptation existing HEI to OE points
 

Dhoo! I can't believe I forgot that one. That's what I did when I removed the HEI from my Burban.

Re: Help clarify harness adaptation existing HEI to OE points
 

Great help all.

That external coil might be the simplest means. I’ll cross reference that number and see what’s the best quality example on RockAuto but it may be that very NAPA item.

If I go with an inline ballast resistor, can you recommend what I need? I imagine the resistance varies and I want to ensure the correct example is in place.

Re: Help clarify harness adaptation existing HEI to OE points
 

IC14SB coil as working without resistor is interesting, I didn't know there was such a thing. I find nothing really technical when searching on the web, just forum posts and some pictures of it from different angles than on NAPA's website showing an imprint on the side about no resistor required. So this seems to be something NAPA would rather not mention.

Re: Help clarify harness adaptation existing HEI to OE points
 

I have used hundreds of them over the years, no problems at all. I use to use the Ecklin coils before they got sooo pricey
https://www.ebay.com/itm/16654367590...3ABFBMlI35mLNj

Re: Help clarify harness adaptation existing HEI to OE points
 

That is a good price

Re: Help clarify harness adaptation existing HEI to OE points
 

I pay that for the IC14SB ones That are imported

Re: Help clarify harness adaptation existing HEI to OE points
 

Great info, I think I'll bookmark this thread.

Re: Help clarify harness adaptation existing HEI to OE points
 

Just buy the coil, you will end up cussing the ballast resistor before it is over
Not the much higher for the coil
I dont have stock in the co, lol Just trying to help

Re: Help clarify harness adaptation existing HEI to OE points
 

This article should help. Basically the difference between 6v coil or a 12 volt coil is what the internal ohm reading of the primary coil windings are. All this confusion started when the automobile went from 6 volts to 12 volts. Instead of making a different coil the manufactures for the most part added resistance to the ignition wire to drop the voltage to the coil. It was cheaper than engineering a new coil and any old coil would work on any car. Plus there was an advantage just down the road.

About the same time engine compression was increasing. The increase in compression lead to more of a voltage drop when cranking the engine over. That voltage drop caused the volt to the coil to drop and in turn the coil putout became weak and the engine was harder to start. To compensate for this the manufactures bypassed the resistor while the starter was cranking so the voltage at the coil was enough to provide strong spark.

https://blog.simonbbc.com/ballast-re...nce-and-coils/

Re: Help clarify harness adaptation existing HEI to OE points
 

That is correct, most coils have 2 oms of resistance the but in these ones have from 3 to 4 oms
This is also the type coil you would need if you put a Pertronix electronic ign in

Re: Help clarify harness adaptation existing HEI to OE points
 

Just got back from Napa with the coil. Shocked that one was in stock and grateful to have but will work real hard to discover one that is not made in the PRC. The parts guy says Echlin has a version of IC14 (no SB) that might not be PRC made but unsure whether or not it needs external resistance.

Happy to report the cap is US made and uses brass not aluminum. The gasket is US made.

Advanced Distributors in Shakopee, MN is rebuilding the points distributor that’s original to the engine. I’ll ask the owner what he recommends for points and rotor.

Good thread guys, I’ve learned a lot so far.

Re: Help clarify harness adaptation existing HEI to OE points
 

All of Ecklin use to be made in the USA now some of it is made in Mexico The last Ecklin points I bought were made in USA

Re: Help clarify harness adaptation existing HEI to OE points
 

I’ll post back what I discover. Another local Napa has that Echlin example in stock (allegedly) and I’ll call about it tomorrow. Will also call Wells tomorrow and inquire where theirs is made. NGK has one too I’ll look more into.

Thinking this spade adapter might be useful and spare me from splicing in a ring terminal at the coil.

Re: Help clarify harness adaptation existing HEI to OE points
 

Fwiw, the Echlin HEI modules I purchased last year were US made.

Re: Help clarify harness adaptation existing HEI to OE points
 

So, by using a 12V coil, you lose the advantage of ignition system bypass wire compensating for voltage drop during start.

Re: Help clarify harness adaptation existing HEI to OE points
 

Here's a Delco parts list for use with a points distributor I'm posting from member 1970CSTBlazer:

"I just rebuilt the original points distributor for my 1970. Here is a list of genuine USA made NOS Delco parts I used to bring it back:

List is for 1972 350 Blazer:

Cap: D308R/ 12338667 OR 1971244
Rotor: D409/1932015
The light duty rotor D426R 1852722 is an option, but I never liked them.
Points: D106P/1931988
Condenser: D204/1932004
Uniset points/condenser: D1007 1876600
Vacuum advance can: 1973437
Coil: D512/1115238"

Re: Help clarify harness adaptation existing HEI to OE points
 

Yes that would be true.