[RodB]

Hi and welcome to the Phorum. That wire running from the changer to the little box is the audio signal cable from the cartridge. Inside the box is a transformer that matches the cartridge to the amplifier. If you have to replace the cartridge, the original was probably a magnetic cartridge so it's important to know the characteristics of the new one in order to keep the transformer happy. The info on the set of schematics at Nostalgia Air shows what you need. Just take your time and enjoy.