Performance Tools, Autozone Brand, PT Digital Multimeter (DMM) Instructions

This is a simple device, but you always lose the one-page manual, even if you put it into your toolbag. This is a short summary of key points, and the manual.

Instructions are here: W2974_Manual.pdf

Excerpts of key points:

Diode Test Mode

The red wire goes to the ANODE. The black wire goes to the CATHODE. The current goes into the ANODE.

ANODE (+)  --|>|--  CATHODE (-) (stripe)

The display will report the voltage drop from the cathode to the anode. Generally, this should be 001.

If the probes are in the wrong direction, it’ll read “1” along the left side. I think this means “infinity” on this multimeter.

Testing the Alternator and Battery

Put the dial to “DCV 20”, 20 Volts DC, and measure across the battery terminals. It should read 14V when the engine is running. This puts charge into the battery.

When the engine is off, it should read around 12V.

Testing a Light Bulb or Fuse

Make sure it’s an incandescent bulb. It has a thin wire in there that’s coiled up.

Remove the bulb and test it with the ohm-meter function. Set the dial to 2000K Ω (2000K Ohm). Setting it high will help avoid false positives from showing very low resistances.

Measure across the leads. It should read no resistance, “000”.

Testing the socket is a little trickier. Generally, car parts run at 12V, so set the meter to 20V DC.

Do something to send power to the socket. It might be turning on the lights. It might be using the turn signal to flash the light.

Put the probes into the holes where the contacts would touch. The voltage should read 12 or -12.

Be careful not to allow the metal parts of the probes to touch. That would cause a short circuit and could blow a fuse or damage equipment. There’s a way to hold the probes with one hand, so they don’t move, and then you move the whole works into the socket.

Determining Which Pin Is Ground

All the light sockets are polarized. One pin is + and the other is -, or ground. The ground connects back to the car body. To determine it, turn the car off, and find a bare metal place on the car body.

Set the meter to 2000K ohms, and measure the resistance between the pin and the body. If it goes to zero, that’s the -. Test pins until you find it.

NOTE THAT YOU SHOULD HAVE THE CAR OFF. If the car is shooting current through the pin, it could damage the meter.

Testing Batteries

You might need to test small batteries like AA batteries.

You can test two things: voltage and current. The meter has a special function to test the current.

First, set the meter to 2000m Volts. Measure, and the readout should be something like: 1506. Since the meter is in “millivolts” mode, that means 1.5 volts. 1506 millivolts = 1.506 volts.

Next, set the meter to the battery test mode. It’s the area that reads “1.5V (4.0mA) 9V(25mA)”.

It should read 4.0mA, which is the current the battery can provide.

A “dead” battery could read something like 1080 millivolts and 3.0 milliamps.

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