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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
    Joined: Mar 21, 2007
    Posts: 484

    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
    Joined: Aug 31, 2006
    Posts: 833

    recardo
    Member
    from Winslow

    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
    Joined: Mar 21, 2007
    Posts: 484

    BigRed390
    Member

    So I don't even need the regulator? :confused:
     
  4. recardo
    Joined: Aug 31, 2006
    Posts: 833

    recardo
    Member
    from Winslow

    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.
     

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

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  6. BigRed390
    Joined: Mar 21, 2007
    Posts: 484

    BigRed390
    Member

    Thanks for the advice! I'm thinking of going with the internally regulated one. Seems MUCH simpler!
     
  7. recardo
    Joined: Aug 31, 2006
    Posts: 833

    recardo
    Member
    from Winslow

    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. 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
    Joined: Aug 31, 2006
    Posts: 833

    recardo
    Member
    from Winslow

    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
    Joined: Jun 25, 2001
    Posts: 3,791

    ray
    Member
    from colorado

    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
    Joined: Oct 7, 2003
    Posts: 4,066

    Levis Classic
    Member

    Interesting approach Ray!
     
  12. Lobucrod
    Joined: Mar 22, 2006
    Posts: 4,122

    Lobucrod
    Alliance Vendor
    from Texas

    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.
     
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  13. recardo
    Joined: Aug 31, 2006
    Posts: 833

    recardo
    Member
    from Winslow

    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
    Joined: Jun 21, 2004
    Posts: 4,446

    joeycarpunk
    Member
    from MN,USA

    Hooked up this way wouldn't it run on after the ignition is shut off?
     
  15. ray
    Joined: Jun 25, 2001
    Posts: 3,791

    ray
    Member
    from colorado

    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
    Joined: Dec 29, 2005
    Posts: 4,222

    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. 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
    Joined: Apr 29, 2006
    Posts: 2,270

    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.
     
    wackdaddy likes this.
  19. joeycarpunk
    Joined: Jun 21, 2004
    Posts: 4,446

    joeycarpunk
    Member
    from MN,USA

    Good info guys thanks.
     
  20. they have been used in billet form on aftermarket kits (well close to a turnbuckle)
     

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  21. Zerk
    Joined: May 26, 2005
    Posts: 1,418

    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
    Joined: Jan 6, 2011
    Posts: 2

    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
     
  23. Livemeyer
    Joined: Aug 24, 2018
    Posts: 6

    Livemeyer

    Hello all, I hope someone can chime in and help as it looks like this is an old thread. Anyway, I'm working on a 51 Chevy truck and currently doing wiring. I have had the truck running for a while now with just basic wiring from battery to starter, ignition switch, HEI distributor, and start button (separate from ignition key). It has a 327 V-8. The alternator is a 3-wire style. Though wiring isn't complete, I was looking to get the alternator hooked up. I ran a wire from the output of the alternator to the battery. Through my reading I discovered that there's a #1 and #2 connector and that #2 is an exciter wire that should be connected to the main output terminal with a short wire.

    Now here's the issue: after hooking up the short wire from #2 to the alternator battery output connector, I came to the truck next day and battery was dead. Was showing 8 volts across the terminals. I charged the battery and checked the alternator and yes it is putting out charge. It was odd, I was seeing 16+ volts. That seems high, even for charging a low battery, especially considering it doesn't have feedback in the system (I haven't run #1 wire to the ignition key yet). After running it a while, I shut it off and got out my battery charger. Some time later, I was working around the alternator and put my hand on it. It was hot. It wasn't running long enough to get that hot. My gut feeling is it was leaking some battery juice to ground. I disconnected the wire from the #2. Now, I've been doing my research and have come up with a number of things to test, which I will do soon. I travel for work and have been away from the truck for a few days. When I return, I hope the battery still have a good charge (I left it on the low charger setting overnight), I will look for parasitic draw, and I will see if hooking up the #1 wire to the ignition key will have a difference. The question is, could this new rebuilt alternator have an issue that would cause a voltage leak? Could it just be that the #1 connector needs to be hooked up to the ignition? (Doesn't make a lot of sense unless it sending voltage and then not sending voltage somehow turns off #2).

    Thank you in advance for your thoughts.

    - Dave
     
  24. squirrel
    Joined: Sep 23, 2004
    Posts: 55,870

    squirrel
    Member

    I think you ought to connect both of those terminals, correctly,
    before you start the engine!
     
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  25. Livemeyer
    Joined: Aug 24, 2018
    Posts: 6

    Livemeyer

    I agree! But I also like to figure out why something is doing something - and if it's right or wrong.
     
  26. squirrel
    Joined: Sep 23, 2004
    Posts: 55,870

    squirrel
    Member

    well, if you have the feedback wire disconnected, you are telling the regulator that it is not producing enough juice, and to crank it up.

    so really, connect all the wires before you run it.
     
    Livemeyer likes this.
  27. Livemeyer
    Joined: Aug 24, 2018
    Posts: 6

    Livemeyer

    Finally! After all the research I've been doing, this is exactly what I wanted to hear. In theory, this makes sense, but nowhere could I find any answer about this! See, everything I was reading was telling me to wire up #2 to the output and #1 to the ignition switch. But the way it was behaving was acting like a short to ground, and I wasn't certain how it could be draining the battery if it wasn't running. There were no written words anywhere saying what it might behave like if the #2 wire was connected without #1. Thanks for confirming my suspicions. I've been on a work road trip and haven't been able to get back to working on the truck in a week. Once I get home I can finish the wiring with the confidence this will be the solution.
     
  28. Livemeyer
    Joined: Aug 24, 2018
    Posts: 6

    Livemeyer

    Jim, so what's the difference to the regulator between the wire going to the keyed ignition in the off position, and there being no wire at #1 at all?
     
  29. squirrel
    Joined: Sep 23, 2004
    Posts: 55,870

    squirrel
    Member

    I don't know. I haven't see the schematics of both type of regulators.
     
  30. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,213

    sunbeam
    Member

    To stop run on hook the exciter wire the accessory terminal
     

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