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    Alternator Problem, need help

    So, I had a problem where the alternator wasn't charging the battery at all, and wasn't putting out any power at all. I figured the alternator was broken, so I picked up another one, but then I realized the battery light on the dashboard was never coming on. So, the problems start here.

    With my old alternator the battery light on the dashboard was never coming on, I have an early 86, so this means the alternator wasn't getting it's startup power so it wasn't working.

    I figured since I had another alternator, I'd have that one tested (took it to autozone, passed) and put it in and see if that fixed it. I also fully charged the battery and had it tested, and it's good too.

    With the new, apparently working alternator in, I still have no light on the dashboard, and it's still not doing shit. I checked the bulb and cluster and they work. I then did the test where you unhook the D+ on the alternator and connect it to ground. The light came on when I did this, so that entire side of the circuit is fine. (Ignition switch, cluster, bulb, wiring harness).

    Now I'm kind of stumped though because if I connect it to the alternator, the light doesn't go on, and it doesn't put out any power when running. Bently shows that the other side of the circuit goes through the starter and then to the battery. My starter works because I can start the car, but should I check these wires anyway? Which ones are they on the starter?

    Also, it shows that both sides of the alternator, the D+ and the other one are connected to two diagnostic port connectors. I checked the voltage at these too. The one on the D+ side (with the cluster light) I get battery voltage, as this is already confirmed to work. I get no voltage between the two, and no voltage on the other side. Was I supposed to?

    What else should I check here? I know that the alternator should be working if the circuit was complete, since the light does work, but there is something wrong somewhere else. It did the same thing with my original alternator, and this one passed the tests so the alternator should be fine.

    I'm ready to drive this thing off a cliff, if it makes it there on battery power

    #2
    Totally off topic... greatest username ever.

    Comment


      #3
      Sounds like you have an open circuit someplace. Using the wiring diagram, trace it out and you'll find the fault.
      The car makes it possible, but the driver makes it happen.
      Jim Levie, Huntsville, AL

      Comment


        #4
        Ok, I just checked out all the circuits in this wiring diagram:



        I have battery voltage on both sides of the alternator now, but the dashboard light still doesn't come on, and it's not charging the battery.

        If I do the test in bently where you disconnect D+ and connect it to ground, the dashboard light does come on.

        Is the only thing left the alternator now, I had it tested but I guess it could still be broken... Are there any grounds or anything that are not in that diagram that could be missing?

        Comment


          #5
          You should check to make sure that the gronds from the engine to the chassis are intact. If they are it sounds like a bad alternator.
          The car makes it possible, but the driver makes it happen.
          Jim Levie, Huntsville, AL

          Comment


            #6
            what voltage do u get when the car is off (on the battery)?

            what voltage reading do u get when the car is on (on the battery)?

            then put the high beams on (while the car is on), and what do you get for voltage then?

            Comment


              #7
              Originally posted by autoXer View Post
              what voltage do u get when the car is off (on the battery)?

              what voltage reading do u get when the car is on (on the battery)?

              then put the high beams on (while the car is on), and what do you get for voltage then?
              ~12v on the battery, each of those things you listed lowers the voltage slightly.

              I'm just going to buy a whole new alternator.

              Comment


                #8
                Bump for this thread, I just experienced same exact issue. Would like to know if anybody had a solution.

                Comment


                  #9
                  Check the ground from the chassis to the oil pan. Also check voltage while running with + on the output of alt, and - on the alt case. If its not 14v, its likely the alt is bad.

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