What year is the Gt 17 and what type of ignition is on the engine.
My older S series Ariens have K series Kohler engines and the safety circuits have long since been removed. They have breaker point style ignitions and I dont know how the safety circuits were originally wired, but I think they were only neutral start switches, no seat switches. I have rewired many tractors with both old style and newer electronic ignitions. Breaker points need battery power or at least alternator/generator power to work. Electronic ignitions on small engines usually create their own power.
If it has electronic ignition, the safety circuit will most likely ground the coil to stop the engine. If you can find the kill wire coming out of the engine, disconnect it and make sure it isnt touching anything and engine should run. Touch that wire to ground and engine will die. Usually if you disconnect any and all wires coming out from under the cowling, the engine should run. Don't disconnect the starter wires or you wont get it to turn over. This applies to electronic ignitions.
If your engine has old school beaker point and automotive round style coil, then it's a different story. To kill these engines, power is removed from the coil at the positive terminal.
Start by identifying your tactor model and serial # on the tag on the front left frame rail. Make sure you have a muti meter with continuity test feature. This will help to test your safety switches when we find the electrical diagram for your specific tractor.
If you think it's the seat switch, find the switch, disconnect the wires, use continuity tester to determine wether switch is normally open or closed by actuaing it by hand with tester connected, then either jump wires or leave wires disconnected to simulate desired state.
Hope this helps