Most of the circuits in lawn and garden tractors use low amperage with the exception of the starting circuit. The wiring also only runs a short distance. I recommend using 6 AWG wire for the high amp starting circuit, and the negative side of the battery to common ground connection. All other wires can be 16 or 14 AWG. The easiest and most effective way to make all of the connections is by using nylon wire crimp connectors. Nylon wire crimp connectors are more durable than ones made from PVC. They are also easier to install than soldered connections. The most common crimp connectors you will use are spade and ring connectors.
To measure AC voltage for example on your engine’s stator, you first locate the two wires coming from the stator. Turn your DMM to AC Voltage. Place the red probe onto one of the wires, and the black probe on the other wire. You should read about 24 to 30 VAC.