How To Test Car Stereo With Multimeter. Connect the red wire on your meter to a pole on the fuse. Leave your battery connected to the car and with the car off connect the red probe of the multimeter to the positive lead on the battery.
For this use the amplifier at VDC mode set the wires check the amp fuse along with output and check the voltage. Learn how to use a digital multimeter to check voltage. All analog audio circuits establish a zero volt DC reference used as the circuit ground.
Introduction to The Multimeter.
A multimeter is the tool to measure these three parameters. To test the voltage first remove the connector at the back of the car stereo. Turn the multimeter knob to DC voltage then touch the black lead on bare metal and red to the wire to be tested. For this use the amplifier at VDC mode set the wires check the amp fuse along with output and check the voltage.

