Cummins Marine Diesel Repower Specialists › Forums › Cummins Marine Engines › Tach stopped working

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  • October 29, 2022 at 2:13 pm #138316

    Robert Oliveira
    Participant

    1990 6BTA 300 M2 with a Prestolite alternator (appears to be one main wire to the Battery, and one other for the tach).

    Port Tach went to zero while underway disabled the glending synch. Both stations read zero. 

    I’ve tried tracing wires but not sure I’m checking the right wires. One wire from Alternator somehow lead to 2 at the VDO tach. 

    Any suggestions how to diagnose? The alternator is charging. 

     

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  • October 30, 2022 at 11:58 am #138336

    Tony Athens
    Moderator
    Vessel Name: Local Banks
    Engines: QSB 6.7 550 HP
    Location: Oxnard, CA
    Country: USA

    Snoop around on google –dozens of after market suppliers– DB  Electric comes to mind..

    October 30, 2022 at 5:58 am #138333

    Robert Oliveira
    Participant

    Options?

    Understand totally. is rebuilding the only option? Or could I buy a replacement?

    October 30, 2022 at 5:00 am #138324

    Tony Athens
    Moderator
    Vessel Name: Local Banks
    Engines: QSB 6.7 550 HP
    Location: Oxnard, CA
    Country: USA

    Loose a bearing in your 22 yrs old alternator and your tach will not be your issue. Remember it spins at 2.5X+ engine rpm and is part of the coolant pump drive– IMO, you are on borrowed time so  do it,  along with the idler that is also part of the belt drive system…

    October 30, 2022 at 4:49 am #138323

    Robert Oliveira
    Participant

    Options?

    Thanks, I figured that would be the best option. Unfortunately I’m in the middle of a trip, so swapping the alternator would probably be easier. Are there no compatible drop ins for my set up? I don’t see anything on your site? Thanks again!! Also, given that charging seems to be working well, I’d really like to try and get the tach circuit working in the mean time. 

    October 30, 2022 at 3:51 am #138322

    Tony Athens
    Moderator
    Vessel Name: Local Banks
    Engines: QSB 6.7 550 HP
    Location: Oxnard, CA
    Country: USA

    The older wiring factory diagrams are on this site

    30+ yr old alternator– Time to take them into a old fashioned alternator shop and have the gone thru top to bottom

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