Here are the facts...
My 2003 Polaris Sportsman 500 starts with the pull starter everytime. Although it cranks and cranks it will not start when using the starter. I first replaced the battery, no good. I have now replaced the starter. Still no good. I tried starting the quad in the dark so I might see anything shorting while using the key start. Nothing. It's been this way for about four months, I still go riding but am forced to use the pull start. Anyone got any suggestions? Thanks.

 

It sounds to me like the ignition switch may be bad. It might be giving you power to the ignition when just turned on but drops power to the ignition when in the start position. That would certainly explain your problem.

 

on that same line, take out the plug and then turn over w/ the key to see if its firing the plug. if not then hes right in what he said.

 

Did u check all wires could be bad ground or like they said. if u know anyone with similar rride try swaping key assemblys and see. could be bad connection inside tumbler