Cooked alternator?

[metallicareload99]

What does it mean when the ammeter pegs out down past -40 (Discharge) when the key in the ignition switch is in the run position, engine is left off intentionally?  When this happens I quickly turn the key to off, don't want to damage my new engine harness.

Now when I disconnect the alternator (dual field and I think it's rated at 45 amps) and turn the key to the run position (engine still left off) the ammeter shows a discharge of only a few amps, what you'd expect.  Headlights, blinkers, and heater motor all work as they should when switched on and the ammeter indicates the load you'd expect for each system.

Background:  my car has had electrical problems since I messed up wiring the alternator with the old engine harness.  I think there was a short at or near the alternator and it toasted one of the field wires and a few others.  Since then the charging system has not worked even after I tried to rewire it and has caused nothing but problems when it is hooked up.  I replaced everything (voltage regulator, engine harness, ignition ECU and coil).  The alternator is the only part I haven't changed out, seems I am still having the same problems.

Given this information, I believe I have isolated my problem to the charging system, specifically the alternator.  Unless something under the dash I have no idea about could be causing these problems.  I going to put in a new alternator and see what that does.  Any of you folks out there have any suggestions?  Thanks for any help

[metallicareload99]

Update:

When the new alternator is installed, and they key is switched to the run position the ammeter only shows a discharge of a few amps.  Hopefully it was the alternator that went bad and was causing all the problems, knock on wood.  Any thoughts?

[2Gunz]

I say you had a bad alternator.

Turn the key on and pay very close attention for smoke, burning smells and rummage around in the wires looking for

anything that is warm.


Passing that find a meter and meter the voltage at the battery with the engine off.

Should be around 11 to 12 volts.

Start the car and meter again with the engine at like 2000 RPM.

Should be around 13-14 volts if the alt is working like it should.


PAY VERY CLOSE ATTENTION to smells, and hot wires.

Buy yourself a fire extinguisher.

And if your are not running a stock alt you need to upgrade the Alt wiring.

good luck.

[Nacho-RT74]

the "damaged" alt could it be JUST THE BRUSH ISOLATOR feeded by blue wire broken , or brush itself making some slight ground contact with chassis or rotor shaft...

Of course also could it be Rotor shorted