308 GT4 Ground Locations | FerrariChat
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308 GT4 Ground Locations

Discussion in '308/328' started by Thomasio, Feb 23, 2020.

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  1. Thomasio

    Thomasio Karting

    Feb 27, 2018
    127
    Full Name:
    Thomas Alberti
    #1 Thomasio, Feb 23, 2020
    Chasing around a strange problem related to the D wire to my alternator... shows 12v with a multimeter, but will not light a NOID light. Alternator will not charge unless I jump 12v directly to the D wire on the alternator.

    Gauge cluster is pulled out, if I jump 12v in to the yellow/green stripe side of the G dash light, I get 12v at the alternator (as verified by NOID light). If I jump 12v in to the other side of the G light, I do not get 12v at the alternator D wire.

    I’m suspecting some voltage back feeding somewhere die to a missing or poor ground.

    I searched but cannot seem to find a thread about ground locations. I verified the ground strap from the engine to the chassis, and I cleaned the ground cable that is at the relay panel.

    Where can I find other ground locations, and is there something else I should be trying?

    Thank you for saving my sanity.
     
  2. Thomasio

    Thomasio Karting

    Feb 27, 2018
    127
    Full Name:
    Thomas Alberti
    #2 Thomasio, Feb 23, 2020
    P.S. the “G” light in the dash is about 60 ohms (or was it 40 ohms), does that seem about right?
     
  3. thorn

    thorn F1 Rookie
    Silver Subscribed

    Aug 7, 2012
    3,324
    Tallahassee, FL
    #3 thorn, Feb 23, 2020
    The case of the alternator provides the ground (to chassis).

    What is your specific problem that led to troubleshoot?
     
  4. Thomasio

    Thomasio Karting

    Feb 27, 2018
    127
    Full Name:
    Thomas Alberti
    #4 Thomasio, Feb 23, 2020
    Alternator was not working after winter storage (and body repaint to original color). Removed alternator and bench tested, with good result.

    The yellow / green stripe wire (“D”) at alternator shows 12v on a multimeter (when disconnected), but drops to 2v when connected. If I jump 12v from battery to alternator, it works perfectly.

    So I began tracing back the yellow/green stripe wire back to the “G” light in the dash

    If I jump 12v to that side of the G light, alternator works. If I jump 12v to the other side of the G light (yellow / black stripe), it does not work.

    Yellow / black stripe goes from the G light directly to the top of the fuse box, 1st fuse location. I see 12v there.
     
  5. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,930
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #5 Steve Magnusson, Feb 23, 2020
    This seems very unusual (and that bulb resistance seems reasonable). My suggestion would be to unplug the GV wire from the alternator, and connect it directly to a ground. Then turn the key "on" (the alternator warning light should illuminate) and make these four voltage measurements (with everything else still plugged in):
    1. GN wire terminal at top of fuse #3 to ground = should be +12V
    2. GN wire terminal at alt warning light to ground = should be +12V
    3. GV wire terminal at alt warning light to ground = should be 0V (or close to that)
    4. GV wire terminal at the alternator to ground = should be 0V since you connected it to ground ;)

    If you pass those 4 tests, and the alternator still doesn't work (with everything hooked back up as normal), we'll have to burn you as a witch. Otherwise, give a shout back for what's what for those tests, and that may give a clue about where to go next.
     
    SamN likes this.

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