My alternator on my '93 7.3 diesel shorted out and caught fire out on the road. Only a couple of wires burned and the serpentine belt and of course the alternator. I'm looking for causes so I can try to prevent this from happening again.

 

On this one, I would have a starter/Alt shop install a new one and test the current draw when the batteries are full and all accesories on. If the batteries are shot and cannot become full then that could have overheated the stator/armature. I think it was just time for it to burn out and it did so more violently than normal.





1986 F-250 6.9 diesel,4x4,XLT Lariat,Ex Cab, 8'bed,etc...

 

When I bought the truck it already had an aftermarket alternator on it. I just want to make sure that there's not something else going on. I'm hoping it's just the alternator. Thanks when I put the new one in, I'll take it and have it tested.

 

I've put Five alternators on my 88/7.3.
I bought the NAPA alternator with a guarentee.

I've never found a reason for the dying alternators. The only thing it could be is an intermitten short, like a frayed wire. One of the Wire's carrying a lot of current.
It's going to be in between the Alt, and the Fused wires. Thinking that a Fused wire would open, where a solid wire would over heat the diodes in the Alt.
My wiring diagram was no help at all, and the wires are very difficult reach.

In your case it sounds like the Battery was supplying the Current. That's about the only thing in your system with enough power to heat the insulation up and start a fire and still have energy left.
It's possible that something in your ALt shorted and the battery was feeding current through that short directly to ground.
Repair the wires, replace the ALt and see what happens.