We have a 93 F-Super Duty diesel fire rescue truck that the Volunteer Dept has been having issues with since before I joined. When I started looking at it, it would not shift gears when in drive so you had to manually **** it to drive it. I noticed that the PCM power fuse was blown and continues to blow. The truck has a leece neville high output alternator on it. One of the wires seems to run to one side of the pcm power fuse. I think this because it puts out 6volts and I’m getting 6volts on one side of that fuse and 12volts on the other side which does t seem right. When I unplug that wire at the alternator, the truck will run drive shift charge etc for about 10 min then stops charging, won’t shift, and the tac drops to zero. Side note, when you first turn the key on, the volt gauge jumps up and down and I hear a loud clicking in the engine bay( I think it’s the glow plugs) Help we don’t have much money and the truck is important to our fleet .. I took the pcm out and looked inside it “appears ok” . I had the alternator tested and it says it’s good. I replaced the tac sensor because it originally was reading 1000 rpm off and now it works right when it works. Weird thing is the truck runs and drives good for 10 min without the darn PCM power fuse even in it .. I’ve tested the pcm relay and it seemed good.