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Discussion in 'Ford Trucks' started by Sharpshooter77, Feb 6, 2007.

  1. Sharpshooter77

    Sharpshooter77 Senior Member
    Messages: 162

    Is it possible that the brushes in an alternator can get stuck and not let the system charge up. I ask this because as I was leaving the parts store and the voltage gauge said 10 to 12 and it usally says 13 to 14 volts . the lights in the dash were very dim and my headlights were also dim. Even when I reved the motor the gauge would not move and the lights stayed dim. But once I hit some bumps in the road very hard it went back to 13 and 14 volts and the lights got nice and bright. This also happened about a week ago. And I did the same thing hit some bumps in the road hard and it made the gauge go back up and the lights were bright again too. So I don't know if its the really cold weather we been having here lately or do I just need a new alternator. The one in there now was replaced May of 2006, I think its still under warrenty. Let know what you guys think. Oh ya the truck is a 1985 F-250 351W, 4BBL. THANKS
  2. Sydenstricker Landscaping

    Sydenstricker Landscaping PlowSite Veteran
    Messages: 3,882

    Check the connections at your alternator, and battery. One could be a little loose and do that.
  3. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    Could be the little wires that lead off your internal voltage regulator to the brushes. I had mine corrode through, they are real light gage copper.Hitting the bumps makes the ends touch again.The alternator was over 5 years old so I replaced it.
  4. theplowmeister

    theplowmeister 2000 Club Member
    from MA
    Messages: 2,515

    how about a bad ground
  5. Sharpshooter77

    Sharpshooter77 Senior Member
    Messages: 162

    I checked all of the connections and they are clean and nice and tight. There are no broken wires. And its working fine now. But now the truck has a anti-freeze leak. The leak has been on going for a while and its a very small leak. So I going to wait for warmer weather or see if i can get it to a shop.
  6. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    The key is when hitting bumps hard it does it.
    That's why I tend to think it's an internal issue with the alternator. Might unplug the alternator when it's not running and look at the plug contacts. The plug can burn up too with all the current flow plowing pulls. Always start with checking connections / cables and put dielectric grease on connections to protect them from crude. There are many ground connections check, clean and grease them all.
    It will just upset you if it's not the alternator after replacing it.
    If you can afford it, upgrade to a higher output alternator if the old one's toast. You can get off the shelf / Internet replacements to fit almost any system. Make sure you have enough room if the new one's a bigger physical size.
  7. snowman3725

    snowman3725 Junior Member
    Messages: 14

    im having the same problem, when i start the voltage gage is low, but after 2 minutes or so of running, it will shoot back up to normal
  8. Mudman78

    Mudman78 Senior Member
    from NJ
    Messages: 103

    85 should have an external voltage regulator mounted on the passenger fender wall. Check the connections and follow the harness to the alternator. There are a couple of places under the electrical tape where two wires are spliced into one and vice-versa. They like to corrode in these locations.
  9. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    I didn't notice he had the still carbed F-250 when I posted my reply.
    I had an 86 Ranger that Ford had gone to EFI and internal regulator that year.
    The big trucks had a bit of a lag on upgrading systems. My 89 still has on the floor dimmer switch.

    If you need to replace the voltage regulator make sure you get the Heavy Duty one.
    The regular duty ones just don't hold up. They are not designed for plowing and constant on status.