The very first thing you should do is post the full model number and serial number found on the chassis data decal.
Once we have something to search with, we may be able to find the wiring diagram online and give you some things to check out. That data decal might be found under the tilting seat, or under the hood.

As mownie said, ditto about model#'s etc.

There are multiple configurations of safety switches on nearly identical tractors. A solution for one can be an entirely different troubleshooting path for another.

IF the mower has an OPR (operator presence relay), your symptom would sound like the 12V going through the seat switch to the relay is being interrupted.
That said, that type system is in the minority, with most of them NOT having 12V through the seat switch.