umm, the front wipers may have a fuse in three places. There are fuses under the steering column on the fire wall, there are fuses behind the kick-panel on the passenger side, and there are fuses in the fuse box under the hood.
Your fuse for the windshield wipers all depends upon the year of your cherokee. For the '84-'96 without intermittent wipers there is no fuse. Instead Jeep used a circuit breaker that is a 5.5A for the '84-'88 and a 7.5A for the '89-'96. If you have a '84-'96 with intermittent wipers then there is a circuit breaker that is 7.5A. It could be that this circuit breaker tripped when you installed the amp and isn't coming back on when you restart the Jeep (I think that is how the circuit breakers in Jeeps work). Or you could have a short in your wiper electrical system that is causing the circuit breaker to trip every time you try to turn on the wipers. I'm not entirely certain where the circuit breakers are but my best guess would be on the fuse box under the steering column.
If you have a '97-later model then the wipers use a 20A circuit breaker that will be in slot #30 on your junction block.
Also, I've had the wipers go out in my '87 Cherokee before becuase the wiper motor loosened where it mounts and was jamming against the firewall. Take off the panel where the wiper motor is and make sure that the system is free to move around.
I am assuming that you only have problems with the front wipers, because the rear wipers are on a completely different system and souldnt be affected by the front wipers going out.
Hope this helps.
-Hunter