I fixed a 2002 zrt 600 with the same problem, turned out to be a combination of a bad key switch and bad bushings in the throttle lever that was making the the safety switches screwy.
What I would do is to eliminate the entire sleds wiring harness by taking and unpluging the rubber 4 wire plug at the stator. There is 3 female connectors and 1 male.
Nothing will work on the sled with that unpluged and you will have to kill it by jumping the 2 wires that are not yellow on the stator plug, that will shut it off..
If it runs fine then the problem is in the sleds electrical and will rule out the electronics
If it looks stock...... It must be ???????