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Alternator not charging

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  • Alternator not charging

    can someone help please, my alternator is not charging the battery on the m3.

    when engine started i get just above 12v and when you put the the car under load light heaters the voltage drops. the battery is good and charged.

    If you rev the engine 3 - 4k rpm then the battery see 13.4v but when you turn the engine off and on again is stop charging.

    there is ground on the alternator, checked from the case to car body, and earth straps around the engine bay, all good.

    the blue wire and the big red battery are connected ok.

    However there is no battery light, on ignition or startup, have checked the bulb and its ok, the parking brake lamp and oil light up ok.

    Can it be the voltage regulator on the alternator (two screws with the black regulator on it) be faulty? any ways to test it?

    How can i test the blue wire?

    I have done a search and checked the tell tale signs but im stuck.
    Any help is very very appreciated.:thank you

  • #2
    Remove the voltage regulator and check the length of the two carbon brushes.

    Do you have the battery light on when you turn the key to "ON" ?
    Is the ABS still functional?



    • #3
      The lenght i would say is low, but if you place the reg in the alternator and slide the reg you can notice the brush touches in side.

      no batttery light when turn on the key.
      abs light lights up then off, if you drive the m3 before the battery drain the abs light glows dim, this is the identifier that the battery is not charging and going to die.

      i also noticed just now on the regulator there is only one contact from the black resistor thingy out/for of the 2 screw holes? surely this is not right?

      - - - - - - - - - - - - - - - - - - - - - - - - - AUTOMERGED! There's no thread "bumping" or "double posting" within a 24hr period. - - - - - - - - - - - - - - - - - - - - - - -

      got a picture

      - - - - - - - - - - - - - - - - - - - - - - - - - AUTOMERGED! There's no thread "bumping" or "double posting" within a 24hr period. - - - - - - - - - - - - - - - - - - - - - - -

      looks like one contact is snapped off, ive not seen one before but can anybody confirm??

      - - - - - - - - - - - - - - - - - - - - - - - - - AUTOMERGED! There's no thread "bumping" or "double posting" within a 24hr period. - - - - - - - - - - - - - - - - - - - - - - -

      hi guys

      changed the regulator today, still no luck

      theres no battery light on inginition turn on or start up.

      Things checke so far

      Battery lamp ok,
      Earth strap ok, can ground from alt case to chasis and red earth wire to engine earth straps, earth is ok
      have battery voltage on big red
      have voltage on blue exciter wire
      new regulator,

      Any fellows have any clue to check anything else?
      Last edited by m3215; 05-19-2008, 07:37 AM. Reason: Automerged Doublepost


      • #4
        The light has to be on for the alternator to begin charging normally. Remove the blue wire from the back of the alternator and ground it. Turn key on , engine off. The light on the dashboard should come on. If it does, you probably need a voltage regulator (or you have an internal problem with the Alt.) If the bulb doesn't light, you have to trace the blue wire back to the instrument cluster. The blue wire goes to cavity 16 of C1. The ignition feed for the bulb comes in at cavity 14 of C1 (green wire) It's also possible there is a bad trace on the printed circuit board. Good Luck



        • #5
          Thanks for reply jimmyC.

          Just like to report It fixed. Alternator internally was the problem, Replaced with new on and It's charging, Even the lights are more Brighter!!

          when i replaced the alt if was exchange bases and they provided one with solid mounts, Then luckily while installing i thought of a post i saw on here about why BMW didn't use solid bushings becuase of the revvy nature of the engine can cause the timing case to crack and got it exchanged back for my original refurbished alt with rubber bushings.

          This forums Great source of info.


          • #6
            Check your brushes or the voltage regulator!
            Fully Restored 1985 Corolla GT-S
            1987 328ci SR20DET Drift Car (Will Convert to M3 Spec soon)
            1989 Honda Civic Si-R Current Project
            2002 Corolla CE Daily Driver



            • #7
              Jimmy's write-up helped me solving my charging issues. Symptoms were no battery, brake fluid level warning light or e-brake warning light (the 3 that should light up) on upon startup, as in key in position 2 i.e. ignition on engine not turning.
              They did light up when I disconnected the blue exciter wires from the alternator and connected them to ground.
              After replacing the brushes and after that the regulator incl. the brushes didn't fix this it turned out to be internal to the alt, just like JimmyC wrote.
              In my case it was intermittent contact of the exciter wires post (D+) and the alternator internals. When I wiggled it I could see the above mentioned lights turn on and off.

              One of the 2 blue exciter wires goes from the alt to the instrument cluster (as JimmyC wrote) and the other goes to terminal 12 in the diagnostics connector.