Quick and dirty guide to using a Multimeter
Learn to fight off those electrical gremlins with this tool
One of the most hated jobs in automotive repair and maintenance is without a doubt, the electrical system. In classic cars (which is what we will discuss here) these systems are not rocket science, but can easily confuse the hell out of you and me.
The most common tool used by us weekend mechanic’s is the current tester, one end goes to a known good ground and the metal tip (the opposite end) to where current should be present, if you got juice, the bulb inside the tester lights up, a quick way if your electronics are getting power, but there is another tool that can help you check for voltage and a few other electrical test procedures, the multimeter.
At first glance, the multimeter can be a little confusing but fear not.
We will look at the Harbor Freight Tools Cen-Tech Digital Multimeter, why? Because it’s cheap, even free if you get the HF Tool coupons, and here at Gearhead Rover we are all about frugality.
How to Check Voltage
When checking a circuit for voltage position the dial on the section marked “DCV” or DC Voltage.
Since we will be working on cars or motorcycles the electrical systems will mostly run on 12 volts, and for that, you will set the dial to the 20 marker on the DCV section.
To check for voltage on a circuit, set the black test lead on a known good ground (i.e. Negative battery post, engine block, bare metal chassis) and the red test lead goes to where ever you are checking for voltage, (i.e. Positive battery post, stereo voltage source, light bulb positive terminal, alternator to battery source lead, etc.)
Once the multimeter detects voltage, you should get a reading of 12 volts or more (if the car is shut off) or 13.5 to 14.5 Volts if the car is running. If no voltage is present, start troubleshooting (blown fuse, bad ground, loose wires, etc.)
Another main troubleshooting tool is measuring resistance. Through resistance, you can know if an ignition coil is bad or the electronic pickup coil on your distributor works properly.
To measure resistance turn the dial to the Ohms reading section marked with the Omega Sign “Ω”, and point it to the 20k marker.
Now, use both the red and black test leads to check resistance, where to position the test leads varies depending on what you are troubleshooting, on an ignition coil you can position the test leads on each outside post to check for the resistance on the primary circuit of the coil. You can set the positive lead on the positive terminal of the coil and the negative lead inside the coil tower to check the secondary circuit. The primary circuit will have a typical value of between 0.4 to 2 ohms and the secondary circuit should have a reading of between 5k to 15k ohms.
You can also check the resistance of electronic ignition systems, but these will vary depending on make and model, so search for your specific application.
The last thing I troubleshoot with a multimeter is continuity, on most multimeters you will have a specific function for this, sadly with the Cen-tech you will not, but we can work around it by using the resistance function. Set the test leads on point A and B of the same wire, if the multimeter registers zero, you have continuity, if you get a 1 or higher then there is a break in continuity.
These are some of the troubleshooting options a multimeter can give us, but by no means does this article tackle all the options this tool can help you with, but it is my intention to get you started down the path of maybe hating working on your cars electrical system a little less.
Hope this has helped you in at least a small way, if you have any comments or suggestions please leave them below,
Until next time, have a good one fellow gearheads.