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Alternator Warning Light

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  • Alternator Warning Light

    I have had a warning light on my port engine go off, and have tried just about everything. I pulled the alternator off and had it tested, and checked the belts-everything is OK there. I put a load tester on all the batteries and found one to be bad-replaced it and still have a warning light. I switched the starboard warning light to the port side(to check for a bad indicator light), and I still have a warning light on the port engine.
    Any ideas as to what I can do next?

    Also, note to Mac.....please make the jumper cables connecting one battery to the next a couple of inches longer. I played hell finding a battery with a similar terminal arrangement to the Deka that the jumper would reach!

  • #2
    Been there/done that

    and had all sorts of fun on boatdiesel w. the Volvo folks.

    Here's my post"
    "Next KAMD 42 P problem - this one should be easy.
    I have an intermittent alternator alarm on one of my 2 1900 hour old alternators.

    No alarm on startup; no alarm while initially running at speed; but when I back off to idle the alarm comes on/goes off with no predictable pattern. Earlier in the season i occured only when the boat was at idle and rocking while drifing a rip so had thought it a loose connection/corroded wire; cleaned everyting and hoped for the best.

    Its getting worse and popped up yesterday 40 miles offshore. I had run out/no alarm till we backed off to idle; shut down both engines and sharked for 5 hours withvarious electronics taking amperage from the battery.

    On startup the alarm came on and stayed on up to 3000 RPM's ate which point it shut off. It then came on and off a couple times on the way in whwen the boat was laboring up the backside of a wave; or once when I tabbed down a bit.

    When the alarm goes off the guage shows 14 volts.

    I have a 4 battery bank which are charged off two alternators through a set of isolators.

    I know this boils down to 1 of 3 things:

    * alternator not putting out at all times * battery not accepting charge * bad wire

    How do I go about isolating this in a sane fashion? Measurements at the dock show 13.8 volts coming out of the alternator and consistent 13.8V on all 4 batteries.

    I have the service manual, have studied it and understand the brown wire off the bottom left stud on the alternatoris the one tha energizes the circuit. I don't understand what goes on in the lectrical box on the engine and where I should be measuring.

    What should I be looking for in terms of voltage on this wire? Can I jumper it (easier said than done) from the alternator all the way up to the alarm input at the helm to see if the wire is the problem?


    and the response:

    The brown wire is a resistor wire to excite the alternator. Once excited it allows a small amount of current to quiet alarm. To eliminate the problem you would go into the electrical junction box on the motor, find your ignition circuit. Install a 3 amp diode in that true ignition lead and attach on the alternator with the brown lead. Batteries should be charging at 14.1-14.2V. Volvo regulators are non adjustable so you get what you get-sounds like 13.8V for you

    The gray wire is your tachometer signal. Typically goes to the terminal marked "W" on the alternator.

    I fought it a long time; talked to the mechanic that pointed out it was one of 3 things - alternator ($$$) - wiring harness ($$$) or Volvo alarm unit ($$) - w/ only half a season left on those engines I did the obvious and cut the wire .

    You might want to try *very* painfully jumpering the good engine harness plug to the bad engine's gauge plug. Its 6 or 8 wires that would have to be jumpered; all in the service manual wiring diagram and that will tell you if its the guage or not.


    • #3
      I took the easy way out.....
      I called the nearest authorized Volvo service center(about an hour away from my boat) and explained the problem to them. They are sending a tech out to take care of it--no expense to me...covered under warranty!