dude i've got a 96 trak and i'm dealing with the same crap.......  i've been un hooking my battery.

You have a different problem. Yours dies while it's off. His dies while running. His alternator is not working obviously for some reason. He said it was tested good so that means it's not getting power to energize the alternator. Only thing I can come up with!

I concour with Amour, also check the idiot light on the dash, if it is burned out some GM alternators will not charge, I had that problem on a old Ford tractor that I changed to 12 volt with a GM alternator.

I concour with Amour, also check the idiot light on the dash, if it is burned out some GM alternators will not charge, I had that problem on a old Ford tractor that I changed to 12 volt with a GM alternator.

First i've heard of that but completly believeable!

I agree its probably in the energizing wire. This wire is typically a switched source and according to the haynes book it first goes from the switch through the IG-COIL METER fuse which is supposed to be 15 amp.  It then splits off in a Y and one side goes straight to the #3 terminal on the alternator.  The other goes through the idiot light and into the #2 terminal on the alternator.  Haynes says these wires will be black and white (black with white stripe? or white with black stripe?) and the one that goes from the idiot light to the alternator is labeled as white and red. 

I tried posting a pic of the diagram but the forum doesn't like me tonight and is giving an error.  So I have uploaded it to my site and you can see the diagram here:

http://www.spyderrobotics.com/images/wiring.jpg

I tried posting a pic of the diagram but the forum doesn't like me tonight and is giving an error.  So I have uploaded it to my site and you can see the diagram here:

http://www.spyderrobotics.com/images/wiring.jpg

thanks sir.