I bought an Ibanez JPM100 P2 and P3 recently, and the P3 (which is very beaten up) sounds drastically different to the P2. It sounds like single coils, not humbuckers. The output jack was a bit funky, so I just replaced it, and hoped that'd fix the issue, but it hasn't. I actually quite like the sound, but the amount of buzz and extra noise isn't practical.
The JPM guitars have a 3 way toggle. Position 1 is supposed to be bridge humbucker, position 2 is the (I think) inner coils, and position 3 is the neck humbucker. Position 2 is much louder than position 1 or 3, which, combined with the single coil-like sound positions 1 and 3 produce, seems like I'm only getting a single coil from each position (hope that makes sense).
The wiring all looks pretty sound, with no obvious bad connections. Does that description give any clues as to what might be the cause of the problem? I can post clips if necessary. The pickups themselves are pretty funky, and even the material DiMarzio use to wrap around them has gone all icky brown. I'm wondering if I just need to buy replacements for everything, switch and pots and all, but it'd be nice not to have to.
Have you checked the wiring at the switch?