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  1. #1
    New User
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    Jun 2017
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    Littlestown, PA ( near Gettysburg)
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    Default Erratic charging system 1986 Mustang Gt

    I posted about this problem a year or two ago with no solution, so it sat unrepaired. Now i am back for another repair.
    I have added a 100 circuit breaker on the two black wires coming from the Alternator so I can easily switch it in, or out of the circuit.
    With the alternator switched OFF, the car starts and runs normally--except that it is not charging the battery
    When the alternator is in the circuit several things happen----the windshield wipers pulse on and off, some lights flash on and off and the engine surges. My guess is that the engine surging is due to the alternator load turning off and on.

    It has a 2G Ford Alternator with the regulator built into the alternator. There are 2 heavy wires that carry the current back to the battery. There is also an "exciter" wire, small gauge that is to send 12V to the Alternator but with the engine off and the key on, I see no voltage on this wire. I believe it should be showing 12V when the key is on to tell the Alternator to provide current to recharge the battery.
    I do not want to put a 12v jumper onto this exciter wire because i am afraid it will backfeed somewhere I don't want it to go. I think I should cut the exciter wire and then jump 12 V to the Alternator side of the wire.
    Does that make sense?
    Then, if that jumper makes the Alternator function, I can find a switched 12X lead from the fuse box and wire the exciter that way.
    Again, am I thinking correctly?

  2. #2
    Moderator wraithracing's Avatar
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    Jun 2010
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    Grand Junction, CO/RR TX
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    Default

    I have always upgraded to the 3G alternators on my Mustangs, so not 100% sure on the wiring differences. Maybe this will help or you may already have this.

    Name:  2G-ALT_wiring (1).gif
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    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

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  3. #3
    New User
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    Jun 2017
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    Default

    Thanks, that is better than the tiny wiring diagram I have.

  4. #4
    New User
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    Jun 2017
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    Default

    Lets add some NEW INFORMATION
    Last week it started and ran perfectly normally--the charging system performed exactly as it should. I must have done a dozen or more starts and it was just fine. I started it again yesterday and again, it was fine.
    I started it this morning and it was fine...until it wasn't. I had driven the car, lowered the top and windows and it performed perfectly. I shut it off for a few minutes and when i went to restart--NOTHING--no clicks, no bells, no nothing. I immediately checked the battery connections and they were fine and then i checked the battery grounds and they were fine, but I did notice something else---the Circuit Breaker on the B+ terminal of the starter solenoid was HOT. My guess was that it was drawing too much current, so i removed it and after it cooled, i reinstalled it and it started--again perfect charging system.
    Drove it back into the garage and tried a few more restarts and it began to be erratic again---same symptoms--1) surging engine, 2) surging ammeter ( probably the cause of the surging engine) 3) flicjering interior lights on the rearview mirror and 4) the WS/W made some sweeps.
    So I am back to square one except now I have seen it work correctly and I know that CB got hot.
    Any ideas?

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