Why doesnt the 4-wheel drive engage on 2000 Polaris magnum?

It could be any number of problems . Start by visually checking the wires running to the hubs on both sides . Then follow the wires up to the connectors , to make sure they are plugged in . Then check the switch that activates the hubs . If the gear indicator is in the speedometer , do the gears and the indicator match . When the machine is in reverse does the indicator show reverse . If it doesn't match then it is the switch that is mounted on the side of the transmission , follow the shift linkage to the trans , the switch is mounted there with an electrical plug that plugs in from the bottom . The four wheel drive will not activate if its not in the proper gear .