rjkehoe

After several attempts at getting a 3 wire alternator to work on my 77 I broke down and installed a single wire 10 SI alternator. 10g wire from bat terminal to positive battery lead and it didn't work. Any tricks or suggestions???

jpatrick636

Let me just ride along with rjkehoe as I am right in the middle of the same project.

As I was told to just hook up the single "battery wire" and discard the other 2, my question is: what exactly do the other two do?

I understand that one is spliced into the battery wire and appears to be general power distribution throughout the car. Is that what you might call the low side of the system? Is that what the 3 wire alternator uses to read voltage drop?

The other (third) wire appears to go to the ignition. What does it do?

I am also a little confused over the fact that the one wire alternator (Powermaster) has a connection that matches the connector for other two wires on the the three wire alternator????

David Ey

I googeled 'altinator wiring gm and there is a bunch of info to read. Here is some.

10SI Alternator Wiring
The 10SI has three terminals (including those with a 1 wire regulator).

The large "BATT" terminal which gets connected to your battery positive. (Or Terminal Post if your vehicle is so equipped).
And a dual terminal connector. (Repair pig-tails for this connector available at any autoparts store. Or, salvage with alternator if pulling the alternator from a vehicle).
The #1 Terminal. (Marked with a "1" on the case)
This terminal is used to connect to the dash warning light.
For the warning light, a lamp is wired in series with a switched voltage source. During normal operation the lamp stays off. If the regulator is damaged, the #1 terminal provides ground, and the warning lamp will light. Usually.
This terminal is also active on 1 wire regulator equipped 10SI alternators.
The #2 Terminal. (Marked with a "2" on the case)
This terminal is used to excite the 10SI into operation. (3-wire 10SI)
It is connected to the battery positive.
For simplicity you can connect the #2 connector pigtail directly to the "batt" terminal on the alternator.
The terminal is present on 1 wire regulators. Used only for those that require the stock connector to fit snugly.
If you are converting from a 3wire 10SI to a 1 wire regulator you can hook up all your stock connectors, and run it as is. However, thats wasted money unless you plan on cleaning out some wiring under your hood.

If the 1 wire is for cleaning out wires, you only need to retain the "BAT" wire. The #1 & #2 terminal wires can be eliminated. Don't be surprised to find that the #2 wire only goes a short way into the harness and spliced into the "BAT" wire.
The 1 wire regulator comes with a dust plug for the #1 & #2 terminals.


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Some other tidbits available from AC Delco for wiring up a 10SI, is wiring package 1870921 (for those 6 to 12volt conversions). This contains the terminal connector AND an extra resistance wire pigtail to connect to the ignition system (don't use a ballast resistor if you use a resistance wire). Also available is an ammeter package (1965400).

Use a voltage guage to monitor your charging system. It will definately give you signs of impending problems. (Bad regulator, failing battery, etc.)

If your looking for a high output unit, keep an eye out for your everyday rebuilt (re-stamped 63amp). In my case, my rebuilt puts out 80amps at high rpm. More than enough for most needs.

High output aside, don't expect your alternator to do anything for you at idle speeds. Alternator output increases with rpm, even a 100amp unit won't put out much more than a 63amp unit at 1000rpm. If your using underdrive pulleys, this may highlight or worsen idle output problems.

Thanks to Jerry (d.j.sherrell@..........net) for pointing out some terminology errors I had in prior versions of this page.




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This information is only intended as an overview and may not include all the necessary information, data, or facts.
Every vehicle is unique, and research for your particular vehicle is recomended.

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Return to the unFAQ List
This Page Created By Alexander M. Bilan (gmguy89@netscape.net)
All Rights Reserved.
June 13, 1997
Revision 1.3 April 5,2003

I'm Batman

Check the archives, I posted links recently discussing why 1-wire alternators aren't a good idea, and how to properly wire a 3-wire setup.

lowbuck72

One wire alts are fine but have 2 shortcomings. First, you can't run a generator light, but the amp gauge in your Vette will still work. Second, you'll get no charging at idle. The system only gets excited when you increase rpm and have an electrical load on the system. I have one-wires on 3 of my cars, with zero problems.

Veet 66

I did the switch from the 3 wire to one wire. What a big mistake. I went back to the 3 wire with the regulator in it. The comment is correct. When you start and idle the car the amp gauge does not show a charge. You have to rev. up the engine to excite it. There is other draw backs as well. There has been discussions on the forum about the pros and cons.

toddalin

I've had ZERO problems with my 100 amp, 1-wire alternator. Sure you have to blip the throttle to about 1,400 rpm ONCE before the system starts charging, but after that, I see no difference from the 3-wire and it DOES charge down to idle..., at least as well as the 3-wire did.

Are you sure that you have a GOOD ground on the case? I actually ran the existing black ground wire to the case rather than just relying on contact through the bolts.

norvalwilhelm

I have a special built 150 amp truck alternator and it is one wire. I have always notice funny things with it and after reading posts on one wire setups I now understand that it is not a good idea for cars with alot of accessories.
I have a good Voltmeter in the car. When I start the car the voltage sits at 14 volts. As each of the accessories is turned on the voltage drops in steps. By the time everything is turned on the voltage can be at 12-13 volts.
Recently I wired the headlights to relays and they draw the voltage directly from the back of the alternator. When the lights are turned on the in car voltage doesn't budge.
I had the alternator tested at the shop and it put out close to the 150 amps so they claim it is not the alternator.
I know that it is a problem with the one wire alternators. They have their reference voltage off the alternator itself. When power draw lowers the voltage under the dash the alternator doesn't see this reduced voltage and continues along as if nothing is wrong. You need to reference the voltage from under the dash not from the alternator.
A one wire alternator is little more then a battery charger. For something with alot of power drawers the 3 wire is better.
I will convert mine to a external reference.

Someone posted this link a while ago and it is worth reading
http://www.madelectrical.com/electri...hreewire.shtml

StickShiftCorvette

I've had no problems with my 40 amp one wire mini alternator. I also run it at half speed with a big pulley. It weighs half what the original did and looks very trick.

0Corvette Engineering

1 wires also need to be reved up to 1200rpm or so before they can self start. I'm not sure of the exact RPM, but they won't start at idle.

jpatrick636

After reading the article posted by Norval (MAD Electric), I am trashing the one wire and going with a three wire.

Anybody interested in a Powermaster chrome 140 amp one wire alternator? New in box.

David Ey

Isn't that a one OR three wire? My powermaster 100 amp was but quit working so I am sending it back and getting a 140 amp. I'll check tomorrow and make sure I'm getting a three wire. Thanks for the alert.

norvalwilhelm

I am not trashing mine. The electrical shop only took a few minutes to convert it from 3 wire to 1 wire so they can convert it back. It only involves reconnecting a few wires.

rcread

My Powermaster 140 amp alternator can be either three wire or one wire. Doesn't yours go both ways?

James

The Power Master 140 amp 10si alternator is advertised as a 1 or a 3 wire alternator but it really is only a one wire alternator. I called them directly and confirmed this with them. I running this alternator and it has been working great! I wired it according to Mad Electrics "New Design". I run a thick wire to distribution point on the firewall. That distribution point is always supplied 14.5 volts from the alternator. From that distribution point is where I connect all of my high current devices. (i.e 2 spal 13 inch fans, Electric fuel pump, MSD box, etc..) Once this alternator is "excited" it is capable of suppling around 80 amps at idle/low speeds and 140 amps at high speeds. The key with a one wire alternator is wiring it correctly to make it work good. Get on Mads web-site it is a great source for all sorts of automotive electrical tips and tricks.

jpatrick636

After reading everything on MAD's web site and talking with Powermaster, this is what I have sermized:

Powermaster 10SI and 12SI one wire alternators have a "dummy" sensor plug. If wired with the factory wiring (as a 3 wire) you still have a one wire. (as stated by James)

The key to using a one wire is having a sufficient wire size from the alternator to the primary distribution terminal. If that wire is sized properly, the voltage drop will be insignificant. A piont the Powermaster rep made was that if you are getting a significant drop between those two points, the sensing wire on a 3 wire system is just compensating for an undersized wire. That brings up another point. In our old cars, with old wires, putting more votlage to the system, to compensate for voltage drop, can over heat the wires and cause other problems, including a fire. This was illustrated to me when I stripped the (factory) wire harness from the alternator back to the fire wall and found several funky splices. One which was obviously overheating, as the connector and the insulator on the wire was burned brown for about two inches.

It's all about the point of regulation. A one wire regulates at the alternator output. A three wire regultates from the point where the sensor wire is connected (usually at the main distribution point). If there is no drop, or the drop can be eliminated, between the alternator and the distribution point, a one wire should have no problems.

I can see where switching to a one wire and using a questionable existing wire from the alternator could cause problems; because the voltage drop is no longer compensated for. However, pumping more current into a system that has too much resistence could cause other problems.

The botton line seems to be, if you are upgrading your alternator, upgrade your wiring.

Well, that's where I am at the moment. That is until more information comes in.

Any more thoughts and/or corrections?

toddalin

Forget crimped splices. These are the points of resistance, especially when corrosion sets in. All connections should be soldered and insulated.

0Corvette Engineering

The Man has a point!

1. Use a big ol wire from the alt to the Distribution point.
2. Do NOT run the big wire to the battery, that is NOT the distribution point.
3. Connect ALL of your accessories to the distribution point. Never connect them to the battery, starter etc.

The distribution point on my '69 is the horn relay. I have a big wire from the horn relay to a fuse block. That is where all my new power is drawn from. Fans, MSD, Fuel pump, choke.

comp

jpatrick636

All that being said, where is the distribution terminal on a 75? It looks to me as though it may be under the brake booster where I can't get at it without removing parts. I hope I'm wrong. Anybody know for sure?

toddalin: Good point about crimped splices!