1998 Audi A4 No wipers, lowbeams, power locks, turn signals

Hello, I recently purchased a 98 A4 Quattro with 100K miles, good service record, runs well, etc. However, the previous owner installed an aftermarket pioneer stereo/navigation unit that "blows fuses" when turned on due to incorrect wiring, which I have not done, as I plan on putting the original stereo back in. I'm wondering if this could be the cause for so many failures. The auto windows, moon roof, and hazards work fine though. My question is whether I can check and replace the fuses myself, and if not, is this a costly fix?