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  1. #1

    Default alternator problems?

    Have a d 1500 Mitsubishi with a KE 80 engine.
    The battery keeps going dead (a new battery).
    The alternator hasn't been checked yet, but is there a likely source ie. fuse link, etc. that could be bad, and if so where is it located.

  2. #2
    Veteran Member Volfandt's Avatar
    Join Date
    Sep 2004
    2004 Kubota BX23, 1966 WheelHorse 856

    Default Re: alternator problems?

    Have you taken a volt/ohm meter, set it to read DC volts and read across the battery terminals while the engines running?

    Normally, a 12v battery will read anywhere from 12 to 12.5 volts with the engine off.
    Once you start it up, you should then read anywhere from 12.6 to 14 volts. It should ALWAYS read more than it did with the engine off and it will always read higher just after the engine is started. It will then taper down as the battery is recharged.

    A somewhat easy tester to make to check for electrical shorts to ground is to take a std 1156 bulb and solder two leads on it approx a foot long. One to the center stob and one to the case. To test if it will light, hold one end to the batterys POS terminal and the other to the NEG terminal. It should lite up brightly!
    Now disconnect the POS battery terminal cable from the battery post and connect one of the leads to it. Take care to keep it away from the battery terminal or any metal surface.

    Take the other lead and secure it to the POS battery terminal. I use a pair of vise grips. You are in effect placing the 1156 bulb in series with the battery & tractors electrical load.

    If the lamp lights with the key off then you've got a circuit shorting to ground somewhere.

    To find the shorting circuit, find your fuses and one at a time unplug a fuse and watch to see if the lamp goes out. If it goes out then you've isolated the circuit. You can then identify where the short is by tracing out all connections, wiring and devices on that circuit.

    If in removing all of the fuses and none extinguish the lamp then find the battery lead to the alternator and disconnect it, if the lamp goes out then the problems in the alt.
    You may also have a separate regulator so you'll have to disconnect it introubleshooting too.

    Generally. shorts can be a bad blocking diode in the alternator or regulator, a skinned wire near a pivot point, a chaffed wire laying on a part of the engine that heats up or even water built up in a head/tail light lens assem.
    A bad ign switch can cause a discharged battery too!

    Sometimes it takes a little time but you should be able to isolate it.

    Good luck

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