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battery/alt help

Discussion in 'Ford Trucks' started by dieselpusher, Jan 25, 2007.

  1. dieselpusher

    dieselpusher Senior Member
    Messages: 208

    hey guys anyone know how to check to see if its my battery or my alternator tahts bad?
    1989 ford bronco fullsize
  2. poncho62

    poncho62 Senior Member
    Messages: 431

    Put a voltmeter accross the battery when its running. If it says 13.5-14 volts the alternator is charging. Turn on a few accessories and see if it goes down much......If it gets below 12 volts, its not putting out enough. Your plow motor will drag it down, but thats pretty normal.

    The battery, you will have to get load tested, or check each cell with a hydrometer.
  3. hydro_37

    hydro_37 PlowSite Veteran
    from iowa
    Messages: 3,790

    Most auto parts stores sell a load tester which will also test your alternator.
  4. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    The big box auto part stores (and most others) will test the system and battery for free. If you have a battery charger put it on the battery and make sure it's fully charged before going.
    If you have a volt ohm meter - your battery should be 12.6 volts not running.
    When running it should be 13.5 -- 14.5 volts. The dash volt gage is just too vague to rely on for this. Check all you connections and cables before you start replacing parts. They may not look dirty until you take them apart.Clean them with wire brush and put dielectric grease on them to protect and preserve the connection. Clean all your BLACK ground wires that connect to the battery , engine , fenders and core support. Bad grounds can cause multiple problems with the engine and charging system.Unplug the alternator and look at the contacts in the plug,they burn up alll the time.
    Check your serpentine belt's wear gage. You may just need a belt. If you don't have a repair manual, the library has them somewhere in the county system.
  5. Oxmow

    Oxmow Senior Member
    Messages: 124

    Quick field test here.

    While the engine is running take off the hot cable to the battery. If the truck dies its your alternator.
  6. poncho62

    poncho62 Senior Member
    Messages: 431

    Quickest way to fry diodes in the alternator, not to mention circutry in todays modern computer systems.........Wasn't so bad in the old days, but I wouldn't do it now.
  7. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    Don't even do that !
    It will run on battery till the voltage is too low - as the alternator Fry's, not to mention the large spark over top a battery venting explosive hydrogen gas.