Low-voltage wiring is mainly used to connect batteries or transformers to low-powered electrical devices. Examples include railroad or racing car sets and LED lights. Sometimes wires get disconnected or damaged, and electricity can’t get to the electrical device. Determining the location of the wiring problem can be difficult, but using a multimeter is a fairly easy method to test low-voltage wiring.
Look on the label on your battery or transformer. You need to know the voltage it produces. Make a mental note of the voltage.
Turn on the power source. This enables you to test if electricity is getting to the low-voltage wires in the first place.
Turn on the multimeter. Set it to read voltage; you do this by rotating the dial or pressing the appropriate button on the meter, depending on the meter model. Multimeters can measure amperes and ohms as well as voltage, so it’s important to set it correctly.
Insert the colored plugs on the end of the wires that connect to the multimeter into the sockets, if they are not already connected. The red plug goes into the red socket and the black plug goes into the black socket. If there are several red sockets, insert the red plug into the red socket marked for voltage; this socket usually is marked with a V.
Place the two sensors on the ends of the red and black wires from the meter onto the terminals on the power source. You must put the red sensor on the terminal labeled “+” and the black sensor onto the terminal labeled with a “-” sign.
Read the meter. It should display a similar voltage as the label on the battery or transformer. If there isn’t a reading, either the battery is dead and needs replacing, or the transformer isn’t working, in which case you must get it checked by a professional.
Check the wires where they connect to the terminals on the power source. Ensure the connections are secure so you know that electricity is flowing from the power source into the wires.
Look at the wire and follow it toward the electrical device to which the wires connect. Look for damage to the wiring. If you find damaged wire, it's best to replace the complete length of wire. Continue to check the wire until you get to the electrical device.
Check that the wires are securely connected to the terminals on the electrical device. Use the multimeter to check if electricity is getting to the device. Place the red and black sensors on the ends of the wires from the meter onto the “+” and “-“ terminals on the electrical device respectively.
Read the meter. The meter should read a similar voltage as the label on the battery or transformer. This means electricity is getting through the wires to your device. If your device isn’t working it’s not the wiring, so it must be the device. If the meter doesn’t indicate a reading, there is an internal fault in the wiring. You have also checked the wire for visible external damage. In this case you need to replace the low-voltage wire.