Charging system running at 12 Volts, alternator good- F350

Discussion in 'Trucks and Trailers' started by JLSLLC, Sep 24, 2012.

  1. JLSLLC

    JLSLLC LawnSite Silver Member
    Posts: 2,735

    Thanks for checking my post out, I have a 1987 f350 dump i just bought. Its a 460 4 speed tank. Im working on it, fixing it up when i can..etc...So the truck has 12v running with no accessories on.. Wont get any higher I had the alternator checked, and it passed. I checked the wiring to the alt and it seems to be newer and in good shape, good connections, and the battery is brand new. It just doesnt seems right to me, ive always seen vehicles charging system run at 14.5 plus Volts... Im thinking of checking the power wire that goes to the starter and battery, see if theres a voltage drop there, and also check grounds and corrosion. Anybody ever run into this?
     
    ericg likes this.
  2. cgaengineer

    cgaengineer LawnSite Fanatic
    Posts: 15,782

    Seems low, is the belt slipping by any chance? Maybe the person who tested it was thinking 12v was good. Needs to 13+ to overcome losses.
    Posted via Mobile Device
     
  3. JLSLLC

    JLSLLC LawnSite Silver Member
    Posts: 2,735


    Thanks for your reply!!:usflag:The belt seems to have nice tension. The volts will not rise on my meter even while raising the rpms.. something doesnt seem right. im going to look at it more in detail when it gets light out!! Especially the wiring!!
     
    ericg likes this.
  4. White Gardens

    White Gardens LawnSite Fanatic
    Posts: 6,783

    If I recall from my deceased 87......

    The 87s still used an external voltage regulator that is known to fail, or the ground wire for the regulator is in a bad spot. If the Alternator is changed the regulator is supposed to be changed also.

    The regulator should be on the wheel well on the passenger side.

    Might want to check it out.


    .......
     
  5. JLSLLC

    JLSLLC LawnSite Silver Member
    Posts: 2,735

    The cables look great, the truck fires up, but i know once it gets cold it wont. The only crummy cable i think at least, is the positive from the battery, it starts the truck but its junky looking, I dont want to run a new battery low. The voltage regulator is on the back of the alt, im starting to lean towards that. Want to test the reg. first before i go buy one. An older gentleman told me years ago you could just replace the regulator.... if its that ill get a whole new alt of course

    Im trying to get it all fixed up before posting up pics:cry:
     
    ericg likes this.
  6. White Gardens

    White Gardens LawnSite Fanatic
    Posts: 6,783

    Are you sure the regulator is on the Alternator? I know that 87 was a crossover year for body style and some components. My 87 had a 6.9 in it and they start putting the 7.3idi in it half-way through the year.

    If you have the external, it will look like this on the fender well.

    [​IMG]

    The external regulator is known to fail, and the ground is usually part of the issues. Guys were known to move the ground wire to either the frame or engine block.


    ........
     

Share This Page