Generally, the sound source and power amplifier of car stereo are integrated together, usually in the center console, and some in the glove box or trunk of the co-pilot.

Frequency dividers are generally available in high-end cars.

Generally, there are two wires from the central control to each speaker, and the speaker itself basically needs no maintenance. If it is broken, replace it with a new one.

So it's mainly audio source and power amplifier.

The principle of power amplifier is similar, but there are several circuits.

There are a little more kinds of audio sources, such as cassette, new universal CD, DVD, SD card, CF card and hard disk.

It is not difficult to find some basic circuits, or find some old ones and take them apart to learn. It's much simpler than TV and radio.

Learn the power supply circuit (the highest failure rate), then learn the power amplifier circuit, and then learn the switching circuit and small signal processing circuit.