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Overcharging FLD120

Discussion in 'Freightliner Forum' started by W Bench Farms, Dec 27, 2022.

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  1. Dec 27, 2022 #1
    W Bench Farms

    W Bench Farms Light Load Member

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    1995 FLD120 with a C15 started overcharging on me last week. At idle would be about 14.5 volts, but anywhere from 15-18 going down the highway at 1600 rpms. Put my spare alternator on yesterday and it's doing the same thing, but not quite as bad. Have 2 groups of 2 batteries that are about 3 years old. Unhooked each group individually thinking may have a bad battery. No change. Was -10 here over the weekend, and 20 yesterday. Started up on its own. Not sure what to check next. Spare alternator was used, but not sure if both could be bad. Have the original going out as it was under warranty.
     
    W Bench Farms, Dec 27, 2022
    W Bench Farms, Dec 27, 2022
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    Another Canadian driver Thanks this.
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  3. Dec 27, 2022 #2
    bad-luck

    bad-luck Road Train Member

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    Have you checked to make sure the guage is not reading incorrectly?
     
    bad-luck, Dec 27, 2022
    bad-luck, Dec 27, 2022
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    Rideandrepair, Another Canadian driver, Dino soar and 1 other person Thank this.
  4. Dec 27, 2022 #3
    blairandgretchen

    blairandgretchen Road Train Member

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    My thought too. Grab a multimeter and see what it reads.
     
    blairandgretchen, Dec 27, 2022
    blairandgretchen, Dec 27, 2022
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  5. Dec 27, 2022 #4
    W Bench Farms

    W Bench Farms Light Load Member

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    Have a 3 way splitter for the lighter that has digital display. Gauge and adaptor both showing high.
     

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    W Bench Farms, Dec 27, 2022
    W Bench Farms, Dec 27, 2022
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    JoeyJunk, Rideandrepair and Another Canadian driver Thank this.
  7. Dec 27, 2022 #5
    skallagrime

    skallagrime Road Train Member

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    Check your grounds, if possible, run a brand new wire from battery to alternator, see if that fixes it.

    Id lean towards your wiring isnt telling the alternator to lower output because its sensing voltage wrong, basing this on 2 seperate alternators doing the same thing
     
    skallagrime, Dec 27, 2022
    skallagrime, Dec 27, 2022
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    JoeyJunk, Rideandrepair and Another Canadian driver Thank this.
  8. Dec 27, 2022 #6
    bad-luck

    bad-luck Road Train Member

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    Like @skallagrime mentioned, check all the battery connections. Also does your truck have an amps gage?
     
    bad-luck, Dec 27, 2022
    bad-luck, Dec 27, 2022
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  9. Dec 27, 2022 #7
    W Bench Farms

    W Bench Farms Light Load Member

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    Next thought it as to replace wiring. This is a one wire alternator. Has a jumper on the two terminals in the top of the case. Need to find where the battery wire is getting power from, as it does not go directly to the battery.

    No amp meter.
     
    W Bench Farms, Dec 27, 2022
    W Bench Farms, Dec 27, 2022
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  10. Dec 27, 2022 #8
    fishonron

    fishonron Medium Load Member

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    You can take the alternator to an AutoZone and they'll bench test it for free.
    Doing that will at least confirm or eliminate that piece of the puzzle.
     
    fishonron, Dec 27, 2022
    fishonron, Dec 27, 2022
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    JoeyJunk, Dino soar and Another Canadian driver Thank this.
  11. Dec 28, 2022 #9
    Rideandrepair

    Rideandrepair Road Train Member

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    I think it goes to the starter. Same as the A/C compressor. Those wires tend to get chafed, broken/shorted around the front of valve cover.
     
    Last edited: Dec 28, 2022
    Rideandrepair, Dec 28, 2022
    Rideandrepair, Dec 28, 2022
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  12. Dec 28, 2022 #10
    Dino soar

    Dino soar Road Train Member

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    It's been awhile since I've been into mine on my truck but at the starter there's a spot where all the power comes together. You'll know it's the right spot because the positive battery cable goes right to it and there's several others that are on that same lug.

    That is the one that runs over to the alternator.
     
    Dino soar, Dec 28, 2022
    Dino soar, Dec 28, 2022
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    JoeyJunk and Rideandrepair Thank this.
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