The seat switch is a normally closed switch which means with no one in the seat the contacts are making a connection. The plug that connects to the switch also has a set of contacts that makes a connection when you pull the connector off the switch so putting a jumper wire does nothing. If you look at the end of the wiring plug you'll see a section in the center that is movable. If you push that back slowly it should lock in the test position. Don't push too hard or you'll push that section all the way out the back of the plug. With it in the test position start the engine and take the brake off. If it stays running the seat switch is bad and should be replaced.