A great feature of many DMM’s is the continuity setting. The continuity function measures resistance, and if there is a complete connection the meter will give an audible beep. If there is no continuity your DMM will show “OL” on the display meaning there is an open line. You can use this to test for electrical shorts in wiring or components. I commonly use this function to quickly test for shorted ignition switches and ignition coils.
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.
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Measuring voltage is one of the most common tests a tractor mechanic will conduct as he troubleshoots a system. The presence of the correct voltage will determine if a component is functioning correctly or not. A common voltage test will be of the battery. A healthy battery should read about 12.5 volts, and a battery that is being charged should measure between 13 and 14.5 volts.