i have a 2000 polaris sportsman 500. when i put it in low gear my neutral light stays on and my 4x4 wont engage. any idea whats happening?

and another problem i have is that its always stuck in three wheel drive, my front right tire is constantly engaged.

 

Has to show gear position,H/L or R to complete the awd circuit. Check the connectors and wires on the transmission gear position switches if it shows neutral while in low range. Both of these switches have been updated also (items 12 and 13) Dirt Cheap Yamaha & Polaris OEM Parts & Accessories – Cycle Parts Warehouse Internal plastic lever may be worn or broken if it's not a wiring problem.
On the one wheel sticking,usually a mechanical problem. Most of the time it's a magnetized armature plate that wont disengage from the strut coil.Changing hub fluid may help. If it doesn't I'd replace plates as a set if it were mine.Usually the other side plate will do the same thing fairly soon.Item #3.Dirt Cheap Yamaha & Polaris OEM Parts & Accessories – Cycle Parts Warehouse