Since you mentioned that the previous owner "hacked it up", it may be tricky to troubelshoot. IIRC, the antennae booster is behind the glove box somewhere. Mark is correct that poor reception would be the symptom of that being disconnected and/or malfunctioning. You may also have a bad antennae connection at the windshield too.
As for the balance/fader issue, it's either a busted head unit control or a wiring issue, which like I said, may be difficult to troubleshoot here on the forum not knowing where we're starting from.
Do all "four" channels of audio work? You should eliminate the easy things first. If not, you're going to need to pull the head unit anyway to do some continuity checks on the wires.
- Darryl
