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oldguy829 01-01-2006 07:09 PM

1 wire or 3 wire alternator???
Our sbc engine has a 3 wire alternator on it, but I'm replacing it when we wire up the car, so we can go 1 or 3. What's the difference? Is one better than the other?

Rob Keller 01-01-2006 07:25 PM

I could be wrong here but the one wire is the "self exciter type"

i hope this helps

SR66 :thumbup:

41willys 01-01-2006 07:52 PM

Go with a one wire...

docvette 01-01-2006 08:08 PM

Doc here, :pimp:

If your of limited Electrical experience, and just want to "Git Er Dun" .. Or space issues..

Then, A one wire is the best way to go..Although it has it's drawbacks..No Direct provision for Lamp or Amp gauge connections..(unless inductively coupled), But you only have One wire and ground to deal with, and you Can ALWAYS use a Voltmeter.

If you go 3 wire internally regulated, you can direct couple an Idiot lamp and AMP integrate it into a stock harness & instrument cluster..It takes a bit more expertise & Time, but nothing earth shattering if you can follow a schematic..and have some basic tools..

A 3 wire External, takes a lot more expertise, because you need to throw a regulator into the mix..and make it all play, but again, If you have some knowledge, you should be able to do it..

They all will perform as advertised, and last about the same, So it really boils down to your personal preference, skill & Tool level possessed.

Doc :pimp:

oldguy829 01-01-2006 08:42 PM

1 wire or 3 wire
Thanks guys.

IgnitionMan 01-01-2006 09:31 PM

OK, on a regular 3 wire late 12SI GM alternator, there is one large wire from the battery to a lug on the rear of the alternator. There are two other terminals on the alternator side, one marked 1 the other marked 2. The terminal 1 isd to be used for a charge light, connected to the charge light circuit. Alternators that are in circuits that have wither a voltmeter or ammeter don't need this charge light circuit to function.

Now, for terminal 2. This terminal is a power source for the internal regulator. In a 3 wire wireup, the number 2 terminal is literally connected to the larfe lug on the rear of the alternator, from the battery. The large wire to the rear lug, and a jumper fdrom there to the number 2 terminal will make the 12SI internally regulated alternators function.

That said, 1 wire 12SI alternators are simply the exact same alternator as a 3 wire, but they use a specially excited regulator designed for industrial, farm and fleet useage. These special regulatos have the large lug to terminal 2 jumper connection INSIDE the alternator. This is the ONLY difference between the 12SI 1 and 3 wire alternators. The number 2 term is connected to the BATT lug either inside or outside the alternator, NOTHING else is different.

12SI alternators are available in 65, 78 and 94 ampere versions.

There is a CS alternator that uses the same type of internally excited alternator, in the smaller overall size. My 1986 GMC Safari van has the 105 amp version.

Early 10SI remote regulator alternators can greatly benefit from using a Wells VR715 regulator. These regulators are electronigc and perform as the later internally regulated 12SI regulators do. Using the Wells regulator will also stop the light fluctuations at idle speeds, lights going from bright to dim to bright to dim. The stock regulators are servo actuated, in essence, they turn the alternator stator on and ott and on and off to regulate voltage production. What is seen in the fluctuating lights is the servos turning the alternator stator on and off and on and off, constantly. The Wells style electronic regulator simply turns the stator on and keeps it on, and when charge volt level reaches a set point of 14.60, the regulator drops excess charge voltage pas the cut off point, to ground, thereby keeping the charge rate and voltage constant, and the alternator gets much less of a workout to do its work.

The stock Delco regulator cap will fit the Wells, making for a stock appearance for restorers.

2-manytoyzs 01-02-2006 12:59 AM

Thats how I wired my jeepster. I got rid of the original problematic alt and regulator and installed a GM 3 wire, then I used a jumper to jump the large terminal (bat) to the #2 terminal. I dont use a gauge or idiot light so I dont need the 3rd wire. I got the rebuilt alt from the parts store for 39.95 and now I have a one wire alt fairly cheap.

malc 01-02-2006 01:18 AM

This question has been done to death on HotRodders.

IgnitionMan 01-02-2006 01:15 PM

Geez...excuse the heck out of me for posting info on it, as I am new here, and now, will no longer post here.


malc 01-02-2006 01:55 PM

Sorry didīnt mean to get at you personally, but if the search feature was used more folks could arm themselves with more info before they posted.
There are several threads covering this very topic, and even though I considered the post "Done to death" I did offer a site comparing 1 and 3 wire alternators.
I see you were online when I began this reply, so donīt go, stay and share your knowledge.

bluesman123 01-02-2006 07:13 PM

Yeah come on, Ignition!! Stay and post. I really liked what you had to say and ended up printing it out. It isn't always just dead easy to search the knowledge base, anyhow. :drunk:

Dave :thumbup:

oldguy829 01-03-2006 09:14 AM

1 wire or 3 wire
Thanks again guys, and for the record; I searched the posts and read over 20
That came up, but didn't quite get what I needed. The link to mad electrical however was just what I was looking for. The beauty of this site is, you get to wade through tons of opinions and points of view and learn enough to make your own informed decisions.
Thanks again.

302 Z28 01-03-2006 11:40 AM

nevermind, answered my own question.


docvette 01-03-2006 05:01 PM

Doc here, :pimp:

So what will be your Choice, and Why did you decide to go that route?

I read that article too..From MAD..It is a Good one!

Doc :pimp:

oldguy829 01-05-2006 10:39 AM

1 wire or 3 wire
Doc. Decided to go 3 wire. We are putting A/C in it, plus a whopping sound system (this is for my 16 year old son), and I have experience with older cars, domestic and foreign, that dim the lights when you let off the gas, so it just seemed like the 3 wire was the ultimate system, and worth my effort to figure out how to wire it. Even if the difference isn't that drastic, I can't believe the "wiring" will be that drastic either.
Thanks again to everyone that contributed to the lesson.

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