What could be wrong with a 1991 Jeep Cherokee if the windshield wipers turn signals radio and fans for air and heat all went out at the same time and you checked the fuses and they were all good?

It sounds like something in the wiring harness or it may be some naked wires touching and shorting out. Look for burn section of wiring around the battery or fuse area. It sounds like you have burned out a fusible link. This can be replaced by some one with a little wiring knowledge.