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
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.
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.
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.