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GM 3 wire alternator wiring diagram

Discussion in 'The Hokey Ass Message Board' started by BigRed390, Aug 10, 2007.

  1. BigRed390
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    BigRed390 Member

    Pulling my hair out trying to get the old boat to run again. It came with a generator, obviously, and somebody installed a GM alternator at one time with an external regulator. That is great and all, but the alternator died. Oh, and it wasn't charging worth a damn when it was on there. They left the generator harness in and I've got about 1000 wires all over the engine bay. :(

    What I'm getting at....

    Does anybody have a wiring diagram for a GM 3 wire alternator? I've looked through books, etc. and even searched in here (only found ford 4 wire stuff.) Any help is appreciated.
  2. recardo
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    recardo Member

    On a three wire you have the #10 output wire. This goes to the junction of the starter and battery cable.

    On the clip, you have a #10 wire and a #16 (or so). Fold the #10 wire over and put a lug on it to connect to the same point as the output wire on the alternator. On the smaller wire, you run this to the Ignition switch and 12 volts. This is the exciter wire. Most people put a diode in the line, or I just put a 12 volt incandescent bulb (jewel light) on the dash to tell me when the alternator crapped out. Wire from ignition switch to light, and light to alternator.

    When the engine starts, you have to goose the throttle, and the alternator light will go out. With a voltmeter and a diode, you will see the voltage jump and stabalize to 14 volts or so after you goose it.
  3. BigRed390
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    BigRed390 Member

    So I don't even need the regulator? :confused:
  4. recardo
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    recardo Member

    Someone (36-3window??) mentioned wiring the exciter to the ACC switch, that way you don't get engine run-on, and you don't need a diode.

    I thought you meant a 3-wire internal regulator alternator. I just run down to the auto store and get a new 3-wire internal, and shit-can all that mechanical regulator crap, unless you're doing a period-piece restore.

    You'll have to wait till I get off work, as my mechanical regualtor stuff is at home. Others may chip in.
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  5. 1oldtimer
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    1oldtimer Member

    you use a '73 and newer gm alt with internal reg.

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  6. BigRed390
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    BigRed390 Member

    Thanks for the advice! I'm thinking of going with the internally regulated one. Seems MUCH simpler!
  7. recardo
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    recardo Member

    On the output wire to the battery/starter terminal put a big maxi-fuse (50 amp or so), or use a #14 wire fusable link in series.

    ALT O---------------fuse--------------------O BATT
  8. cyclopsblown34
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    cyclopsblown34 Member

    This is the reason I am a member of so many forums. Threads like this remind me of why I joined here. All these great helpful responses are awesome.
  9. recardo
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    recardo Member

    I got home to look at my cheat sheet...

    By the way, GM had two mechanical regulators. One was for generators and a different one was for alternators.

    The alternator one has 4 connections (besides the case needing to be grounded). Left to right, they are: F, 2, 3, 4. The generator one only had 3 connections.

    Normally people just tie 3 and 4 together and route it to the ignition switch and the ballast resistor (if you have points) #16 wire is good enough.

    F and 2 go to F and R on the alternator. The external regulated alternators might be marked 1 and 2 now, which was F and R in the old days.
  10. ray
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    ray Member

    i always run 3 wire alt's as a one wire. hook up a #10 wire or so from the main terminal to the batt as usual, then a short jumper from the #2 terminal to the main lug on the back of the alt to energize it. if the alt craps out, i rely on my volt gauge to tell me.
  11. Levis Classic
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    Levis Classic Member

    Interesting approach Ray!
  12. Lobucrod
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    Lobucrod
    ALLIANCE MEMBER

    That will work fine Ray, just have to rev it up a bit to excite the regulator to get it charging. If the #1 terminal is hooked up correctly it will charge as soon as the engine starts.
  13. recardo
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    recardo Member

    I think the deal is there, that you have to disconnect your battery after you put it in the garage when you don't use the #1 connection.

    My understanding of the #1 connection, is to shut down the alternator when the motor is off. If you don't hook it up the battery discharges through the alternator.

    This is what I've been told, so I don't want to sound like an engineer expert or anything.
  14. joeycarpunk
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    joeycarpunk Member

    Hooked up this way wouldn't it run on after the ignition is shut off?
  15. ray
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    ray Member

    maybe, i dunno, never had a problem with dead batteries, i do it this way on nearly every car i drive, some pretty infrequently without an issue, but you may very well be right. this method has been brought up a few times in the past when the topic of alternators has come up, nobody has pointed this out yet.

    joeycarpunk, no it doesn't run on.
  16. Da Tinman
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    Da Tinman Member

    I run the exciter wire to the r side of the starter seleniod. It turns the alernator on, does not have to have constant voltage. The output wire gets loop to the big wire on the plug in. It won't run on doing it this way. GM alternator will self excite but it needs to be above 2500 rpm ( I think) to do so.
  17. 1oldtimer
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    1oldtimer Member

    not really, if the #1 isn't hooked up it will shut off with the key. the #1 wire id for the warning light (the light acts like a resistor), it needs the little voltage to start (excite) the charging at idle. if the #1 wire is not hooked up then it won't charge until it sees some rpms. the only time it WON'T shut off with the key is if the #1 wire is hooked up to a NON keyed battery source (like the bat lug on the back of the alt) and then it will also stay energized and drain the battery. i for one love the warning lights, you can get a small one and it won't clutter up the dash. my mocked up dash with warning lights (you can buy higher rated senders so there is no need to worry).


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  18. lewislynn
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    lewislynn Member

    Here's a site with everything you'll want to know about GM alternators...I don't think they are still in business but if they are or aren't I want to thank them for making the information available

    I used their info for retrofitting my 56 F100 and it was so simple, using the existing wiring, it almost made me feel pretty stupid.
    http://www.madelectrical.com/electrical-tech.shtml

    By the way, has anyone else ever used a turnbuckle for an adjusting arm on their alternator? I couldn't find anything with the right arc that would work on my old 223 so I just used a turnbuckle with a locknut on one side so it can't vibrate loose...it works great.
  19. joeycarpunk
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    joeycarpunk Member

    Good info guys thanks.
  20. 1oldtimer
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    1oldtimer Member

    they have been used in billet form on aftermarket kits (well close to a turnbuckle)

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  21. Zerk
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    Zerk Member

    I used a pretty stout turnbuckle for an alternator mount once. It worked great, had to grind the eyes flat on the mounting faces, and used a jam nut on the righthand thread side.
  22. slimone2
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    Dolan Springs Az

    slimone2 Member

    Hi Guys, I have a 78 Chevy pickup ,just put in a 97 5.7 vortec, and had a think its a 100 amp alt off a 88 buick century, 3 wire if you only count the wires in the plug on it plus a 10ga.red wire on the back. Now I used the red 12ga wire out of the plugto go to the back connector and the red 10ga wire that was there to start with. The 16ga brown wire in the middle of the plug connected up to the brown wire that was to the original alt plug (the one that was in the truck to start with) Now the last wire in the plug I just taped off did nothing with it. started truck and checked charge with meter an shows charging 14.2 an with every thing on shows 13.6, Maybe I did it right ? Never have been good at the electric on these things ,Can make them run an go fast tho. Thanks for any advice Slimone2

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