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512BBi tach

Discussion in 'Boxers/TR/M' started by nelson, May 14, 2012.

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  1. nelson

    nelson Rookie

    Mar 10, 2011
    19
    CT
    Full Name:
    Nelson Heumann
    #1 nelson, May 14, 2012
    Last edited by a moderator: Sep 7, 2017
    I'm the new owner of an '84 BBi, 47975, whose tach does not work. The car has a Jacobs Electronics, FC3000 ignition in place of the Dinoplex. I'm trying to track down the problem. I have a workshop manual, but the wiring diagram is not very readable. Would anyone have a decent diagram I can get?
    Thx
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  2. alhbln

    alhbln Formula 3
    Consultant Owner

    Mar 4, 2008
    1,749
    Berlin, Germany
    Full Name:
    Adrian
    #2 alhbln, May 18, 2012
    I don't have a readable wiring diagram either, but the tach wire color is marrone (brown). The wire goes from the tach to the Dinoplex connector terminal #5 (top middle) in the factory wiring. It should be wired to the dedicated tach output of the Jacobs 3000. Wiring the tach directly to the coil can damage it.
     
  3. CarbBoxer

    CarbBoxer Formula Junior

    Oct 7, 2008
    844
    Houston
    Full Name:
    PW
    #3 CarbBoxer, May 18, 2012
    I can vouch that the wiring diagrams from

    http://ferrariwiring.com/

    are worth every cent. For $30 you can download the Boxer diagram (and others if you want).

    I have the Boxer one on the garage wall and a folded up one in the glove box.
     
  4. 2dinos

    2dinos F1 Rookie

    Jan 13, 2007
    3,019
    #4 2dinos, May 18, 2012
    Be sure to check the calibration. Mine was off by ~400 revs or so and I was trying to use it to set the idle speed. It wasted a bit of time!
     
  5. nelson

    nelson Rookie

    Mar 10, 2011
    19
    CT
    Full Name:
    Nelson Heumann
    #5 nelson, May 24, 2012
    Thanks for the help. The FC3000 ignition box had a brown tach wire that had come loose. Once I reconnected it to the wire from the tach, it started working, although it seems to be reading high. I think it must be set up for an 8 cyl.
    Nelson
     
  6. alhbln

    alhbln Formula 3
    Consultant Owner

    Mar 4, 2008
    1,749
    Berlin, Germany
    Full Name:
    Adrian
    #6 alhbln, May 24, 2012
    You (or your workshop) could do a quick check with a digital timing light featuring a RPM display (Equus 3568 as example) to see how far it is off. If the tachs display varies more than 5% at 5000 RPM or 10% below 3000 RPM, it would make sense to send it to a shop for recalibration.
     

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