Every Good toolbox should have a couple different types of Electrical Testers. For testing if electricity is present at a wall outlet you may want to use a non-contact electrical tester pen that costs about $10 and can sense electricity within a shielded wire and will light up to tell you the circuit is hot. This is very similar to a timing light that is used in cars that senses the electricity from your coil when it is attached to a spark plug wire and flashes a light on your timing marks found on your harmonic balancer.
But if you want to test exactly what voltage and amperage is present in an electrical circuit you need some type of meter that will allow the electricity to pass through and then provide you more detailed information.
Multimeters provide two basic tests. They can tell you the volts that are being passed through a circuit or they can tell you the resistance in the circuit of voltage passing through it.
OHMs Resistance Testing is important because it can tell you if a wire or circuit is open meaning a wire is cut somewhere along the path or if the wire is malfunctioning. When you set your tester to OHMs and connect it to opposite sides of a wire you should have a reading of near zero. Some wires have built in resistance such as the internal wires of a car’s Coil which will show some resistance because of the length of the wire inside the coil. You can also think of this as a long electrical extension cord wire. The longer the wire the more the resistance. Some circuits also have resistors in them and this can also be tested if you know the manufacturers settings. A Broken Wire will show infinity resistance meaning no electricity can pass through the circuit.
Voltage Testing is the second test that you can perform with a Multimeter. Testers should be able to provide readings in both DC and AC voltage.
Home electrical circuits are normally AC current while most Automotive and battery operated devices rely on DC voltage.
Automotive circuits would be set to 12 volt DC and this would allow you to test if your Alternator is charging your battery. Charging of a battery by a good Alternator will produce between 13 and 15 volts.
Home circuits are normally 110 volts for general lighting and outlets or 220 volts for larger appliances like stoves and furnaces.
Specialty Testers are available for Automotive and Home electrical Circuits.
You can plugin an outlet polarity tester and it can quickly tell you if the wires in your circuit are crossed.
Special automotive testers can provide information like Dwell for your Timing Circuit, Computer readout information and specific tests for many different devices.
Sizes of Multimeters
Multimeters can be purchased in hand held units for under $50 to floor and bench testers that can run into the thousands of dollars. For most home and automotive testing you can rely on a good hand held model that will require a battery. If you are working in a business setting a larger tester that can perform specialized tests may be better and it will need to be plugged in.
Don’t go overboard when purchasing your first Multimeter. You will see some portable models that are very expensive but do not provide more tests then an in expensive $50 model. Also you should stick with Digital Multimeters. Although I personally still use two analog meters from time to time because i need the manual adjustment override a digital readout is often more accurate and easier to read quickly.
Note: When Diagnosing electrical circuits you should first have information about the circuit you are testing to know the settings to use on your tester. You should also know what readings you should expect by information provided by the manufacture of the item you are trying to fix.