This is your basic tractor wiring diagram. There are entirely too many different setups to even begin drawing or posting all of them on this website. The above diagram will give you an at a glance idea of how a tractor is wired up. The more bells and whistles on a tractor, the more wires and switches and relays. For example, the new garden tractors that have and electic PTO and a mow in reverse bypass switch. This setup requires the safety wiring system to run through the PTO switch and the introduction of a relay or two to allow the tractor to move backwards without killing the mowing deck or the engine.
The thing in the middle is the Ignition Swtich. Here are the designations for the letters:
When you turn and hold the key in the Start position to crank the engine over, the Battery and Start contacts touch to light up the Start terminal. When you release the key, they no longer touch and the Battery and Aux. contacts touch and the Magneto and Ground contacts break contact, to allow the engine to run. When you turn the engine off, the Ground and Magneto contacts touch, killing the engine and the Battery and Aux. contacts break contact to turn off the lights for anti-afterfire solenoid.
The Red wire from the stator is the DC circuit. This wire has a diode in it and it charges the battery. The black wire is the AC circuit and it does not have a diode. This circuit runs the light and electic PTO, if equipped.