The purpose of the seat switch is to make sure the operator doesn't get off the mower with the blades running. If the switch is not working correctly. It will kill the engine when you turn the deck on. You check the switch for continuity with a multimeter. Or make a jumper wire to temporarily bypass the switch. I just fixed this problem on an old Snapper Yard Cruiser. One of many problems it had with the deck.Assume im stupid.. how/where do i check this? if the switch was in fact bad, how would that affect just turning the mower on/off and getting on/off it. thanks