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westend's avatar
westend
Explorer
Aug 27, 2015

Ford Superduty battery and charging issue

Yesterday, I had my small utility trailer on the hitch of my 2003 F-250. I had dropped the trailer off and then put it back on the ball. Since it was near nightfall, I checked for running lights on the trailer. No luck. I messed with the 4X connector for a bit and finally gave up, choosing to leave the trailer until daylight. On the way home, the battery indicator and ABS indicator lit up on the dash display. I stopped the truck to inspect and barely got it restarted. I made it another two miles and the truck would not run.

This morning, I went back to truck with a fully charged battery, installed it, and made the 5 mile drive to home. All indicator lamps are now off but measuring across battery posts with engine running, I'm seeing 12.3V.

All symptoms point toward a failed alternator but this charging system has been flawless for 11 years. Is it possible that I blew a fusible link or some other circuit interruption instead of a failed alternator?

Anyone have any diagnostic tips for me?

36 Replies

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  • NinerBikes's avatar
    NinerBikes
    Explorer
    Aug 27, 2015
    My basic test was start the motor up, then disconnect the negative side of the battery. Does it still run? Alternator is good, could be the voltage regulator. Does the motor die? Alternator is probably bad, test for output voltage and amperage, as well as voltage regulator.
  • westend's avatar
    westend
    Explorer
    Aug 27, 2015
    donn0128 wrote:
    Continuity? Naw. Test voltage on both sides.
    Same,same.
    Just so happens my Fluke clamp meter isn't working so will have to do some surgery to get some measurements across the links. I'll try for the least invasive method. Nearly all the wires in the engine compartment are loomed from connector to connector.
  • westend's avatar
    westend
    Explorer
    Aug 27, 2015
    Thanks for the replies.
    With engine running, measurement from alternator stud (red terminal insulator) to ground is .245V.

    I so want this to be a bad fusible link or relay instead of failed alternator. The coincident trailer light manipulations where I left the headlights on for a few minutes right before the issues with the truck, is either a red herring or is the root.

    This afternoon, when I have transportation, I'll take the alternator to the local parts distributor and have them test the alternator. Maybe there's some way I can test for continuity across the fusible links in the interim.
  • Matt_Colie's avatar
    Matt_Colie
    Explorer II
    Aug 27, 2015
    West,

    On an 14yo truck, anything is possible.
    You don't give a hint where you are, but there are lots of simple things that could be the problem.

    Get a meter, get the truck charged enough to start and watch the battery voltage. If it goes up, maybe the alternator is not your problem. Once it is running, put the meter on the stud on the alternator. If it is making power, that is not your problem. If it isn't, it is time for a rebuilt.

    Good Luck

    Matt
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Aug 27, 2015
    Oh it has to wear out sometime. It chose THEN. Nothing wrong with what you did. Reminds me of my mother years ago when she picked up the phone to make a call. The phone chose to ring and the receiver hit the ceiling. Boy was she mad!

    If you wish to check all the underhood fuses before replacing the relic. The 6G is not cheap. See how much your Ford dealer wants for a reman.

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