Assuming you're talking about a lawn tractor, the engine must be turned off before you can bypass the ignition switch. To do this, locate the kill switch on the engine. This is usually a red lever near the carburetor. Push and hold in the lever until the engine stops. Once the engine is off, remove the key from the ignition switch and put it in your pocket. Next, locate the wires coming from the ignition switch and disconnect them. You can use a pair of needle nose pliers to do this. Finally, twist each wire together and tape them with electrical tape.