Mower runs, dies when clutch released.

I have a Craftsman LT 100 mower, bought in 2001 and used every year since. Currently has 636 hours on it. This year it starts easily, but when the clutch is let out the engine dies, like a kill switch was engaged. Does this in every gear including neutral (not hydrostatic), and /or when the blade is engaged. I suspect one of the safety switches is bad, but other than the seat switch, don't know where they are located. By the way, the Kohler Command 18hp engine, always run on synthetic oil, has never missed a beat.

It is the seat switch or the pto switch.
nothing else in that circuit.

A poster last week had ants nesting in his switch.