A friend's 1993 Cherokee died suddenly on the highway and was towed to a shop.
Tech there said that there was a dead short blowing the 20A fuse that feeds the Ignition, ECM, etc. (Blew twice when replaced)
Tech checked the thing over, including the alternator but found no short.
Replaced the fuse again, and everything is now functioning perfectly, and the problem can not be duplicated. Perhaps there was something he did in looking at things that moved the problem point out of contact, but
I don't want her driving the beast until this problem has been resolved, so she doesn't get stranded somewhere.

I have the service manual and wiring diagrams, but am hoping someone may have seen this before, and give me a hint as to which subsystem it may be in and how to find it.

Am I correct in assuming that it must be a circuit with no intervening fuse before the short location? Ignition switch? Corrosion or rubbed insulation?