Old noma mower dies when mower deck is turned on

I posted this question on tractor talk, no replies so I posted same question here.
I have an old Noma riding mower from TSC. It older than dirt. It has all 4 wheels in a
grave, just haven't covered her up you. This old girl has a v twin 16 hp vanguard
briggs. It runs fine for her age. Tenant calls and says something is wrong. It would
start and run just fine. When you apply power to the electric mower clutch, it shut off.
I removed the shroud, discovered one cylinder was choked with dirt. I found the kill
wire going to the two ignition modules. I removed the kill wire from switch. Started
engine, turned on the mower clutch and problem solved. Turn key off, 2 seconds later the
solenoid in carb shuts off the gas and engine dies.
Now which safety switch is bad?

The most likely cause of problem is seat safety sw loose/broken internally,on most tractors the seat sw completes ign kill grounding circuit thru all safety sw's/operating sw's(pto,clutch/brake,parking brake sw's)if seat sw loose in mount,not being actuated by seat or broken internally it's telling tractor nobody sitting on seat,kill eng ign if pto turned on or clutch/brake pedal relased.

You got it Joe. If the seat is falling apart and water gets into the switch...by by. Time for a new seat. DO NOT bypass the switch. Pain in the butt and not a good idea.

Joe, if the seat switch is bad, would it start and run just fine? Only dies when power is applied to clutch.

On many tractors the contacts that are wired into ign kill circuit are fed from the seat sw & the contacts in pto sw & clutch/brake pedel are normally open when pto sw in off position & clutch pedel depressed/locked down,if the contacts in seat sw don't open when sitting in seat due to a loose,broken or bad sw this will supply a ground to pto sw & clutch sw,when pto sw turned on or clutch released the normally open contacts in either sw will close completing ign kill circuit stopping eng,same as turning ign sw to off/stop position,as long as pto sw in off position & clutch depressed tractor will start & eng will run normal.

I noticed the female plug under the seat on one of my riding lawn mowers, don't remember which. The mfgr. deliberately wired it so that it is setup reverse to what common sense would indicate.....trying to keep you and me from disabling it and helping to help us in protecting us from ourselves with our thinking that the switch closes upon sitting in the seat and this grounds the ignition coil.

Well not so. I was looking at the plug one day trying to rationalize why it didn't do as I thought it should and looking closely found a little clip, thin piece of metal stamped with tabs on it that would slide down alongside the terminals in the connector, that had been pushed down into the thing connecting some wires together,,,a couple wires, don't remember that part, but there was a foreign object deliberately placed in the connector. I pulled it out and could do as I wanted initially.

Now before you guys start worrying about my safety, I disabled the engine kill function, not the engage solenoid for the blade. If I get off the seat and have the PTO ON the blade stops. I just got tired of the PIA of having to restart every time I got off to clear something ahead of me.

Mark