Military Vehicle Repair: Generator light, neg terminal, blown fuse

Question
I just installed a new alternator on the driver side and it is puting out 13.9 volts at idle but the gen 1 lite does not go out. In fact as I increase the engine speed it seems to get brighter. The old alternator would make the gen 1 lite flicker  and would sometime get a little brighter. It had a loose connection for the battery cable wire so I installed this new one. This is on a M1008. Thanks, Joe.

Answer
Hello Joseph,
13.9 is just a little bit low...I would like 14 to 14.5 volts.
Are you sure the belt is tight?

There should be a wire from the neg terminal on the drivers side alternator, connected to the engine ground.
And there is another wire, in addition to the pos red wire. It should have 12 volts when the ignition is turned on, and it is the exciter wire.
If it doesn't have voltage, check for a loose or blown fuse under the dash.

You can jump voltage from the batt terminal to that exciter plug, just to check the alternator, but I'll bet it is ok, and you are just not getting ignition to that third wire.

The alternators are interchangeable, by the way. Just don't ground the passengers side alternator neg terminal to the engine. It connects to 12 volts.

Van