Hey guys, newbie here looking for help

Hey everyone, this is my first time on the forum and in need of some help. This might be a long post but I wanna give the run down on what I have and my issues.
I just picked up a 1997 Honda trx300fw for $600. bucks. The quad is in excellent shape cosmetically. No rust or cracks in plastic etc, etc. The old guy I bought it off of bought it brand new in 97. About 4 years ago he had it in the shed and was going to go riding and pulled it out and it wouldn’t start. Mice ate the wiring harness and got into the air filter as well. Instead of fixing it he went out and bought a brand new rancher. He literally left it right outside the shed for 4 years in the weather. Well now the quad won’t move and the motor is locked up. I’m not to worried about the motor end as I’ve rebuilt many quads in the past. (all 2wd drive though)
My main concern at this point is why it’s not moving. It does rock back and forth a little so I’m thinking it’s not the brakes. I can only get the shifter to click up or down 2 clicks. I’m not sure if I’m even in neutral. My game plan was to fix the harness and hook the battery up to see if I’m in neutral with the dash light. All the way down on this quad is neutral, right? Is that a good starting point or does anyone have any other ideas or known issues with my situation? I don’t mind freshening up the top end, (hopefully the crank is ok and could free her up) but I’m not really looking forward to splitting the cases. Any help would be appreciated. Thanks