Hi. I just bought a used JTV-59 that is in mint condition except the 3-way selector switch selects the same thing in the outer and middle positions (outer meaning away from the pickups). This is true regardless of whether I'm using the magnetic pickups or the modeling options, and is the same regardless of which selection switch option is active (i.e., from pushing down the tuning knob). I've also experienced the middle position being dead once; wiggling it restored the (incorrect) selection. Based on this I'm guessing either the switch is bad or there's a bad solder connection.
I've searched through the forums and seen lots of issues where the selector switch works for the magnetic pickups but not the modeling options or vice-versa, but haven't seen this particular problem posted.