My son has a 1993 Isuzu Bighorn 3.1D that has developed an issue with the engine not stopping when the key is turned off and withdrawn.
The only way to kill it, is to remove the 15A Ign/ Eng fuse. Checked Ignition Switch with multimeter at that fuse supply side and switched key... powers on & off.
So some feed-back to supply side of Fuse?
The Alternater was replace a couple months ago with the same model and apart from that not a lot has been done to it.