The ignition circuit consists of your battery, ignition switch, ignition coil, breaker points, condenser, and spark plug. When your ignition switch is turned in the “start” and “run” position, the “I” or ignition terminal is energized and power flows from the battery through the primary winding of the ignition coil through the points and back to the engine ground. The primary winding of the ignition coil are the two small terminals marked + (positive) and – (negative). A small gauge wire goes from the ignition switch and connects to the + positive terminal of the ignition coil. The breaker points and condenser are both connected to the – (negative) terminal of the ignition coil. Your spark plug cable is connected to the secondary terminal which is the large wire port in the top of the ignition coil. Your spark plug is then connected to the high tension spark plug cable and screwed into your engine’s combustion chamber.
Let’s say you attempt to start your tractor and your starter does not engage. No click of the solenoid, nothing happens at all. Before assuming your starter is bad, grab your DMM and set it to DC Volts. Remove the wire going to the small terminal of your starter solenoid and connect the red probe of your DMM to the wire. Now connect your black probe to a ground. Turn your tractor’s key. Your DMM reads no voltage. This tells you that power is not going from your battery to the solenoid. Next remove the wires from the back of your ignition switch that are connected to the “B” and “S” terminals on your switch. Set your DMM to Continuity and connect your probes to the “B” and “S” terminals of the switch. Turn your tractor’s key and if there is no “beep” you know your ignition switch has a short internally and should be replaced.
A common ground is a path for electricity to flow back to the negative side of the battery. Most systems use the conductive metal on the engine block and tractor frame to lead electricity back to the negative side of the battery.
The charging circuit consists of your battery, ignition switch, rectifier/regulator, and stator. When your engine is operating, your stator produces an alternating current by means of electromagnetic induction. This alternating current is fed to your rectifier/regulator by two wires. These two stator wires connect to the AC – and AC + terminals on the rectifier/regulator. The rectifier/regulator converts the alternating current into a direct current and is fed out of it through the terminal marked B+. This wire leads to the “rectifier or R” terminal on your ignition switch. This direct current charges your battery.