[Dave01]

There should be 3 interupts on the starter circuit, the brake safety switch, the seat safety switch, and the pto safety switch. That tractor is old enough to not have a reverse safety, plus even if it did it would only shut off the pto, not the engine. Here's what I'd do. First, though least likely, hold the key to start and flip the pto switch on and off and wiggle it, just to be sure that's not the problem. Next, again holding the key to start, bounce on the seat a bit. In my experience the seat switch is the most prone to problems. If you fold the seat forward you'll see a bar with the 2 seat springs on it, the switch is under that, you can hear it click when you push down on the bar with your hand.

My 2084, very close to the identical machine electrically, has an intermittant start problem. I've ignored it because I just turn the key a few times and it starts. I don't know if it's ignition switch or starter solenoid, but I do know it has nothing to do with the safeties. So, it's possible you have a problem with power running through the key switch not energizing the solenoid.