When I went to use the ac one day the fan stopped working, so I replaced the resistor and it worked until I turned on the ac and the resistor blew. So I started looking around and found the AC belt was broken and replaced that then replaced the resistor and it's been fine since. So that's twice that I powered up the AC with the broken belt and it blew the resistor. I know that the AC switch, at least, and the blower motor are on the same circuit but have no idea why those would be related.
Just thought I would post here for food for thought. Our Isuzu isn't a P'up as it's a 1995 but I think they have a lot in common.