How to use a Multimeter: Using the Ammeter - Purkeys

Purkeys Electrical Tool Kit comes with a variety of useful tools to help technicians test and diagnose heavy-duty vehicle electrical systems. One of the most commonly used tools in the kit is the multimeter, a device that combines multiple electrical diagnosis functions into one portable unit. However, many technicians do not recognize the utility of its ammeter function.

Every fleet has at least one truck that always seems to have problems starting after it has been inactive. This could be caused by either a parasitic load or a defective battery. By using the ammeter function on the multimeter, technicians can accurately troubleshoot the issue.
In the video above, Purkeys National Truck & Fleet Representative, Larry Rambeaux, demonstrates how to find a parasitic load using the ammeter. The first thing he does is plug the red lead into the 10 amp port and set the dial to the 10 amp ammeter function. He notes that if a technician is using a multimeter on a truck, they will have to break the circuit so the current is flowing through the multimeter.

It is important for technicians to know what the ammeter should be reading and what the readings mean. Once technicians confirm there is a parasitic load, they can start pulling fuses to isolate the issue and find out which circuit the parasitic load is on.

Technicians may not constantly use the ammeter function, but it can help avoid misdiagnosing issues.