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Thread: alternator light is on, ignition is off

  1. #1
    noradiator
    Guest

    alternator light is on, ignition is off

    I recently installed a rebuilt Marchal Alternator and a used voltage regulator. It replaced a Motorola.
    After doing the installation, and connecting the batteries, the alternator light went on. When I switched on the ignition, or started the car, the light goes off.

    The voltage reg. gets extremely hot after a few minutes.

    Where did I go wrong??

    By the way, which Alternator is better Motorola, Marchal, Bosch?

  2. #2
    Smadman
    Guest

    regulator is likely shot...

    The risk of used parts I'm afraid. If the light is on without the ignition turned a diode is quite likely punched through. As for the alternators I don't have the experience to know.

    Good luck.

  3. #3
    Roland Kunz
    Guest

    alternator

    Hello

    I remember that the SEV alternator should not run with the Bosch regulator and vice versa but but got supstitutet by the same aftermarked units.

    Not to forget there are different SEV regulators for different alternators ( 500, 900 and 770 Watt )

    Grüsse

  4. #4
    Quote Originally Posted by Smadman View Post
    The risk of used parts I'm afraid. If the light is on without the ignition turned a diode is quite likely punched through. As for the alternators I don't have the experience to know.

    Good luck.
    Hi I have the same problem, so I understand, do you mean a diode is shot on the alternator?
    Thanks

  5. #5
    Senior Member M_deJong's Avatar
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    I would suspect the voltage regulator. Bad diodes in the alternator would result in a low/no charge situation. Light on with ignition off means the voltage regulator is routing battery voltage back thru the field coil circuit due to an internal short circuit.

    Let's review your symptoms to be clear:

    Ignition off, light glows
    Ignition on, light off?
    Engine running, light off?
    Voltage at battery with engine running above idle?
    Last edited by M_deJong; 07-07-2012 at 01:13 PM.
    Mike de Jong | '71 911T/E 2.4 Tangerine | '74 911S 3.2 Ice Green

  6. #6
    Quote Originally Posted by the911Tprocess View Post
    Hi I have the same problem, so I understand, do you mean a diode is shot on the alternator?
    Thanks
    Yes, if the battery light is on with the ignition off (with the key out, hanging on a peg on the wall) then one of the alternator diodes has failed. Only fix is to press in a new one: have the alternator rebuilt.
    1966 911 #304065 Irischgruen

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