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Thread: Charging issue

  1. #1

    Default Charging issue

    I have an 84 t bird 5.0. Car has been having a issue with what I thought was the alternator. Car start fine first crank, runs good but slowly the lights get dimmer until eventually the car will shut off. I thought it would be the alternator. Been through 3 rebuilt alternators now from parts stores and have the same issue. I tested the alt by removing the battery cable with the car running and it shuts off (I know it can be bad for the car). I checked over all the wiring and everything seems to be in the right place. Car runs far to well until the battery dies for the wiring to be an issue. Could it be the voltage regulator or am I that unlucky with these rebuilt alternators? Or any other ideas? Pulling my hair out here.thanks in advance

  2. #2
    FEP Super Member gr79's Avatar
    Join Date
    Jun 2009
    SE Michigan


    Check the alt wiring harness. Its 34 years old.
    Use test meter, light, or unwrap all the tape for visual inspection.
    Make up a temp harness to bypassing the current one.
    Could do one wire at a time. Wiring is like plumbing.
    If alt charges, problem found.

    Had similar issue back in the 80's.
    One day, no charging, alt, battery, reg, connectors, checked good.
    No visual clues of anything amiss.

    Took it to Ford dealer. Asked for engine compartment wiring check.
    They found burnt choke assy and wire. Charged battery.
    Drove it home 25 miles in daylight. Everything seemed fine.
    Next afternoon, set out for work. Made it 25 miles.
    Radio would not even play.

    Having left early, had time before start of work 2 miles away.
    Something told me to unwrap the entire alt to reg harness.
    Yup- Found one bad section in the middle. Insulation melted off both wires. A short.
    Did side of road triage with electrical tape.
    Got engine started, forget how. Charged up fine again.
    Soon after, made up a new harness.
    Never happened again.

    Guess is the shorted choke wire spiked the alt output and fried the wires.
    Choke wire ran direct from alt. Ford did not fuse that wire. I did.
    Dealer dropped the ball and i let them know that.

  3. #3


    That’s a good point I’ll look into that. I chased the wires from the alt to the regulator and they were all in the correct spots. My other thought was if the voltage regulator grounds to the chassis like the starter selnoid if so it could be making bad contact. Also going to check the fuseable links out. The alt terminal labeled BAT lit up a test light with the car not on. About all I had time for today. Will check it out again tomorrow

  4. #4
    FEP Power Member Ray Dog's Avatar
    Join Date
    Dec 2013


    Best easy check of alternator operation is to remember to charge you need a voltage output over 12.5 volts.
    With the car running read voltage at the battery with a volt meter, it should be around 13.5 to 14 volts.
    Then star loading the alt by turning on lights and heat/ AC on full. When operating all these items a healthy charging system
    will maintain an output of 13 or more volts. Anything over 14.5 is over charging. And that will cook the battery.
    If it fails this then look a what gr75 noted about harness issues.
    Also check the health of the battery with a load tester.
    86 Mustang LX 3.8 Convertible (bought new
    84 Capri (needs help)
    05 Volvo XC90 DD( The Swedish Tank)...................Used to own
    08 Magnum (The Roadie Wagon)...........................Too many. the good ones
    95 Saturn SL2 (Kid's Ride).................................65 Chevelle SS, 69 Torino GT
    94 Saturn SL2 (now parts for above) ................39 Willys Overland, 69 Fleetwood, 86 Saab 900
    65 Galaxie 500 XL 390 auto (Waiting for funds)..81 Mustang T-Roof hatch, 88 Lincoln LSC,

  5. #5


    Check the alt plug. It uses two 10 gauge wires spliced into a single 10 gauge wire. The connector melts and can look fine, but crumble apart when you touch it. It could also be the fuseable link near the starter solinoid. This is where that single 10 gauge cable connects.
    2 1986 cougars (both 4 eyed and 5.0)
    1 1987 cougar

  6. #6


    Ps, there should be a resistor in the th ave cluster for the battery light. If the battery lightbulb is burned out, it will put a Lot of load on the resistor and can burn it out. Sounds stupid, but the car could not charge because the bulb in the instrument cluster is burned out
    2 1986 cougars (both 4 eyed and 5.0)
    1 1987 cougar

  7. #7


    All very good info that I will check here shortly. The battery light is always on in instrument cluster though.

  8. #8


    So I went and checked some more of the wiring. The fuseable links are all getting power on both sides. The wires going to the regulator I tested with a test light. Yellow wire always has power. The green/red wire has power when in the run position. The white/black wires have power when the car is running and idling only. And the orange wire with the blueish stripe lights up a test light very dim only when the car is running. Name:  BEBA67C2-1AEC-47CE-B557-253659B087F9.jpg
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  9. #9
    FEP Super Member gr79's Avatar
    Join Date
    Jun 2009
    SE Michigan


    At least the wire colors are not faded yet.
    Regulator connector looks crooked, not seated all the way on one end. The orange wire end.
    According to schematics of regulator connector, that is alt field terminal 'F'.
    Next to it is 'S', alt stator terminal, white wires. Light and gauge connect differently here.
    Yellow is 'A', alt battery terminal.
    Opposite end green/red wire is 'I', key switch acc.
    These should be labeled on the reg and connector for correct index match up..

    Cars with warning light are wired slightly different than ones with amp gauge.
    Some regulators work only with lights, some with gauge, most do both.
    Some wires are not used or connected differently.
    Disconnect connector and check regulator terminals for corrosion.
    Could always buy a new connector and splice it in.
    I did that once. Mis-connected a wire. No charging. Corrected that. Forgot which one.

    Then there are voltage drop tests alt to battery.
    One test checks positive side wiring.
    One test checks negative side wiring.

    Did a search 'ford alternator terminal b has 12v engine off'.
    And one 'ford external regulator wiring gauge or light'
    Lots of images diagrams and articles.

  10. #10


    Just to restate the importance of what gr79 stated. Check that Alternator harness over REALLY good. The black with orange stripe large gauge wire heading over to the solenoid is a known failure point that will cause weak/no charge conditions as gt79 suspects. Tug on it and make sure it doesn't just pull out of the connector. It may be just HALF broken.

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