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Wednesday, August 31, 2016

2001 dodge ram 1500 5.2 alternator not working

I'm working on a friends truck that the battery keeps dying. He got another alt from the salvage yard and its doing the same thing as the original. The gauge in the dash will read about 13 volts while idling but if you take it for a drive the check gauges light will come on and the charging gauge will drop as far as it can. it has power to the main feed from the battery to the alt but not to the two smaller wires plugged into the back of the alt. any ideas?


If this is one of the type of alternators that has the integral
regulator built-in, there should be a place where you can insert a
Phillips screwdriver or small metal rod to ground a tab on the
regulator to force the alternator to put out full current. If it has
that and it doesn't put out full current at a higher than normal
voltage (should be over 14 volts, could be close to 15 volts), then
the alternator is at fault. If it does put out that voltage and higher
current then perhaps the regulator is faulty if the voltage doesn't
stay around 13.5 volts when the alternator is running without using
this trick to test the alternator.

You can get a decent current tester like this one:

to check current. It clips over the battery cable. If you reverse the
connection it will reverse the direction on the meter, so make sure
you're reading current output from the alternator. The smaller channel
on the rear of the tester is for lower amperage readings. The larger
one is for starting current.

Is the battery in good condition? Does it hold a charge?


  1. Yes we had the battery and the salvage alternator tested at autozone and they said both were good. I believe the problem lies in the two smaller wires going into the back of the alternator. neither one of them has power to them when running. i guess what Im looking for is a wiring diagram so i can know where those two wires go

  2. Before I would go to the trouble of tracing the wiring, I would
    suggest making sure the connection for those smaller wires is very
    clean on both the socket and the plug.

    I was pulling my hair out on a wheelchair lift motor that suddently
    stopped working. I had voltage at the rear of my truck but the motor
    would not run plugged into the harness directly, bypassing the
    switches. It turned out it was a poor ground connection. The high
    resistance let me see voltage in the back but it was so high no
    significant current coudl be drawn.

    My solution was to get rid of the ground connection, and while I was
    at it, the positive connection to the fusebox, and wire directly to
    the battery terminals, adding an inline fuse in the positive wire very
    close to the battery terminal. Works like a charm now and I don't have
    to buy a new motor at $350!!! I used side terminal extenders to make
    the connection, about $4 or $5 each.

    If your connector has a high resistance connection (dirty contacts),
    it might not be working correctly. One of those might be to put the
    battery voltage on the alternator either as a voltage sensing wire or
    as that and power to the battery for charging (might do double duty).
    Not sure what the other wire might be for though.

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