alternator check

Discussion in 'Fox 5.0 Mustang Tech' started by sheff2720, Dec 8, 2003.


  1. sheff2720

    sheff2720 New Member

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    about 2 weeks ago my 5.0 wouldnt start.. so i replaced the starter and i figured while i was doing that i might as well replace the battery cause its a fairly new car to me and the battery was looking pretty old.. so this fixed my problem.. and i havnt had another problem until this morning when i went to start it and it wouldnt even crank.. i wasnt getting and electrical signals.. so now im thinkin the alternator may be the problem.. how would u go about checking to see if the aternator is bad?
  2. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Most auto parts store will check your alternator/battery for free.

    For starter problems, here's a checklist:

    Check battery, terminal connections, ground, starter relay switch (also known as solenoid) and starter in that order.

    A voltmeter is handy if you are familiar with how to use it to find bad connections. Measure the voltage drop across a connection: more than .5 volts across a connection indicates a problem.

    1.) Will the car start if it is jumped? Then clean battery terminals and check battery.

    2.) Check the battery to engine block ground, and the ground behind the engine to the firewall.

    3.) Then pull the small push on connector (red wire) off the starter relay (Looks like it is stuck on a screw) and jump it to the terminal that is connected to the battery. If it starts, the relay is good and your problem is in the rest of the circuit.

    4.) Remember to check the ignition switch, neutral safety switch on auto trans and the clutch safety switch on manual trans cars. If they are good, then the relay is bad.

    5.) Jump the big terminals on the starter relay next to the battery with a screwdriver - watch out for the sparks! If the engine cranks, the starter and power wiring is good. The starter relay is also known as a starter solenoid.

    6.) The starter may be hung, loosen up the bolts that hold it on, and give it a good whack with a big hammer. Tighten up the bolts and try again.
  3. Cue-Ball

    Cue-Ball New Member

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    I assume that when you say you "wasnt getting and electrical signals" that means that the battery was dead. IE: nothing electrical would work (dome light, instruments, radio, etc). I also will assume that you didn't leave the lights on or anything like that.

    If that's the case, it's very likely that your alternator is causing the battery to drain. My red LX had this same problem. The quickest way to determine if this is the problem is to charge the battery, then use an ammeter to check for an amperage draw on the battery. Anything over .5 amps is too much. If you don't have an ammeter, or you're really lazy, try this: Charge up the battery and check the voltage. Make sure you've got 11.5V or so. Disconnect the two plugs from the alternator but leave everything else on the car connected. Leave the car overnight and check it in the morning. If you've still got voltage at the battery then the alternator is causing the drain. If that's the case, use this opportunity to upgrade to a 130 amp G3 and you probably won't have any more problems afterwards.
  4. sheff2720

    sheff2720 New Member

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