Does a car stereo amplifier take up one of the input jacks from the CD deck?

Yes, a car stereo amplifier typically requires a connection to the head unit (CD deck) using one of its output jacks. This connection allows the amplifier to receive audio signals from the head unit, which it then amplifies for the speakers. It's important to ensure the amplifier is compatible with the head unit and that the correct RCA output jacks are used if applicable.