Originally Posted by panthermark
The factory speakers are 2 ohms. (I tested mine at 2.7 ohms actually).
But that should not kill the sub. Sounds like they wired them out of phase.
I don't think he actually meant the subwoofer quit, but that the bass was really low. So, I think the amp can't drive the four ohm speakers, and there's the possibility that they were wired out of phase.
If this was my Jeep, I would yank the factory system and start over. But it isn't, and I highly recommend a mom and pop shop that had been rated highly in internet reviews.