Wiring an LS Alternator to the Original 3 Wire Factory Alternator Harness

[CRM318]

I am finishing up an LS swap on my 1979 K5 Blazer and I am stumped as to how I wire the 1 wire, 4 pin plug to the existing 3 wire harness. On the original harness, I have a red and brown wire in a 2 blade connector and the power wire with the eyelet. I assume the power wire goes on the alternator stud, but am I supposed to splice the yellow wire to one of the red/brown wires, or do I set them aside and run the yellow wire 12 a switched 12V sources? I'm using a Holley Terminator X Max system, but the instructions do not mention at all of the alternator. I do have a resistor soldered into the yellow wire.

 

[Babaganoosh]

where did you get the plug from? The Holley harness has a “power tap” connector near the I/O wires to plug in.

I got mine from sloppy mechanics

 

[JoshHefnerX]

What are you using for a computer?

 

[Babaganoosh]

What are you using for a computer?

He’s using a Holley terminator x. They don’t list in the instructions cause it’s a “offroad ecu” and made as a universal harness.

 

[shady]

I believe the brown wire on the factory harness gets hooked to that yellow one on the new plug.
Then yeah the red probably goes to the stud if the wasn't a stud on the factory alt.

 

[CRM318]

Do you mean the red spade in the connector or the red wire with the eyelet?

 

[shady]

Didn't even see the ring lug one lol.

 

[shady]

I don't know what the red one in the plug does.
That last few I've done the alt on, the brown wire is what I hooked up to excite the wiring.

 

[Blue85]

I am stumped as to how I wire the 1 wire, 4 pin plug to the existing 3 wire harness.

You shouldn't have to. Doesn't that yellow wire come from the Holley harness? Just plug it in and go.

The 2-pin harness is for sense voltage and to turn on the "gen" light in the dash. I think jumpering the 2 together would keep the light off and not drain the battery, but it might be worth some experiments.

The 4-pins are Sense, Field, Light, Pulse. You can look up the purpose of them if you want, but you only need the L for the alternator to run. So you could splice the old L wire to the new one and that would kill 2 birds with one stone, but if Holley brought you a switched ignition with resistor, that will do the job as-is.

 

[shady]

The Holley harness doesn't have anything for the alt in it.

 

[Babaganoosh]

The Holley harness doesn't have anything for the alt in it.

You can plug it into the "Power tap" connector on the harness. This is what I did, single wire running to the alternator with the plug.

https://www.sloppymechanics.com/products/holley-plug-and-play-flex-fuel-alternator-combo-harness

 

[CRM318]

I went to a near by speed shop today that specializes in LS swaps. They said that I can splice into the existing brown excite wire or any key on 12V source.

 

[TheDorkKnight]

Another idea

https://documents.holley.com/fb15db59c4e49b413d60e6fbaa98bd3b06077628.pdf