Measuring resistance can indicate the health of a component. For example we can determine if an ignition coil is healthy or not by measuring the resistance of its windings. To measure resistance, set your meter to Ω ohms resistance. If you need to select a range, select the smallest range normally 200 ohms. Place the red probe onto one of the small terminals of the ignition coil, and the black one on the remaining small terminal. Your resistance will then display. A normal ignition coil should read about 3.5 to 4 ohms. If your meter reads a much higher resistance it means your ignition coil may have a short and is faulty.
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.
Think of this as electrical volume. Amps can be determined by taking your voltage (12 volts) and dividing it by the resistance of a load. This is illustrated with the following formula: A = V/R
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.