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Bad Alternator? Need Help.

Discussion in 'Commercial Snow Removal' started by Jason Pallas, Dec 16, 2001.

  1. Jason Pallas

    Jason Pallas Senior Member
    Messages: 662

    I need to know a good test to tell if my alternator needs replacing. Ford Ranger 4cyl.
    Truck runs good - no visible drain on electrical system no dim lights, etc..). Starts fine, runs for long periods of time (let it idle for about 25 min in the drive). Plow pumps runs strong and doesn't drain or stall engine - vehicle re-starts good after running plow for a while.
    HOWEVER, the in - dash volt meter hovers around 8-9 volts (should usually be 12-13 volts) and the idiot light for the battery is illuminated. If I disconnect the battery (neg or postive) the truck stalls immediately.
    Someone told me that this could be the starter relay switch and I did have to jump (bypass) the switch to start it just recently.
    Does anyone know how I can test to see if the alternator is bad or if it's just the starter relay switch that need replacing? Thanks in advance for the help.
  2. Kent Lawns

    Kent Lawns PlowSite.com Veteran
    Messages: 315

    Voltage regulator.
  3. CT18fireman

    CT18fireman Banned
    Messages: 2,133

    Disconnecting your battery while the engine is running is a good way to kill an alternator or voltage regulator.

    Does it hover there at idle after using the plow or all the time? Does it come up at higher engine speeds?
  4. SlimJim Z71

    SlimJim Z71 PlowSite.com Addict
    Messages: 1,031

    I would pull your alternator out, and run it up to the nearest parts store. They'll test it for you, usually for free, and let you know whats going on with it. That would be the best route to go at this time of the year. On a 4-cylinder, it shouldn't be too hard. Better to be safe than sorry...

    Messages: 81

    Thats what I'd do. Pull it out and ask the parts store to test it.They'll do it for free.Then go from there
  6. Jason Pallas

    Jason Pallas Senior Member
    Messages: 662

    It doesn't waiver hardly at all - not after using the plow, lights, etc.... It just stays at a constant 8-9 volts - only budging a small bit - just enough to let me know that it's not broke/stuck.

    The voltage regulator - is that usually up on the firewall on the driver's side?

  7. plowking35

    plowking35 2000 Club Member
    from SE CT
    Messages: 2,923

    Take your multi meter, and with the engine off see what you ahve voltage at the batt terminals. Next start the verhicle and see what you have, usualy volts are around 14 volts.
    If that is what you have the alt is ok. Load the battery, that will give you an idea if its up to par.

    Messages: 81

    Not sure about a Ranger. I think most regulators are mounted to the fender well.Follow the positive lead .
  9. Jason Pallas

    Jason Pallas Senior Member
    Messages: 662

    The battery is at about 12 volts w/o engine running and about 13-14 with the engine running. That's why I tend to think the alternator is probably OK.

    Does the starter relay switch also work as the voltage regulator? I Know that some makes (Late 70's Dodges) had a separate voltage reg/ballast switch up on the firewall. The Ranger is an '89. Thanks
  10. CT18fireman

    CT18fireman Banned
    Messages: 2,133

    Doesn't sound like a voltage problem. Could be a problem with the guage or idiot light or something else in the dash. If the battery is getting 13-14 volts then it is charging.

    The starting problem may be because the solenoid is going out. Replace it.
  11. John DiMartino

    John DiMartino PlowSite.com Veteran
    Messages: 2,154

    I agree with Dino,start it and see if you have 14 voltswith it running,if so,its charging,your guage is reading wrong,either is bad or the wiring to it has a connection problem somewhere.For the money,Id take the truck to a local shop with a load tester,they can hook up an amp probe,and test the alternator output,diodes in the alternator ,as well as load test the battery,and test the starter for excessive draw, all in under 1 minute,so thats what id so if you dont have the time/tools/know how to do it.This way you know if its good or bad,without guessing,or replacing pefectly good parts.
  12. Tommy10plows

    Tommy10plows Senior Member
    Messages: 345

    Bad alternator

    Hmm, does it sound like an alternator problem or a grounding problem?

    The idiot light glows because the field is feeding voltage to it. Check all your ground wires, starting at the battery. Ford cables have two wires coming off the negative terminal, one # 4 going to the motor or frame, and the other to supply ground to other points. Make sure your battery terminals are clean, no corrosion on the terminals, and that they are tight. Then check the grounding from the dashboard cluster to the firewall.

    Make sure you have a good ground from the alternator case to the motor, dirt, grease, leaking oil, etc. affect grounds, so everything should be clean and tight.

    Turn the key on, all accessories off. check the voltage at the battery, that is your base voltage. Start your motor, let it run for 4 minutes, no accessories on at all - that means no lights, no foot on the brakes, heater fan off, read the voltage at the battery. then check the voltage at the alternator, pull negative from the alternator case, positive from the "A" screw head. Should be no more than 2.5 volts above the base voltage. If you are over that you could have high resistance in the ground path, bad wire etc.

    Only reasons you will show the idiot light and an overvoltage condition on are shorted alternator rotor, regulator or wiring. Check all you will find your problem.

    Some ford gas gauges are run from a step down voltage taken from the voltmeter. Does your gas gauge work as it should?

    Finally, a battery cell that shorts under load will also cause this. You should not think that the battery is ok just because it starts your car. Check that too.