What does the audio fuse do in a car?
A car radio will have at least one fuse to protect the unit from things like power surges or other electrical issues. If too much current is sent to the audio system, this fuse will blow out and disconnect the circuit to save the main radio.
How do I know if my audio fuse is blown?
Remove the fuse from its holder. In some cases you may need a small screwdriver to unscrew the fuse holder cap. Look at the fuse wire. If there is a visible gap in the wire or a dark or metallic smear inside the glass then the fuse is blown and needs to be replaced.