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Kenwood Midi System M-45 - System Control Cord

I have been given most of a Kenwood system - amp, tuner, GE, cassette deck. They don't appear to be able to work stand-alone (the amp supplies 16V AC to most of the units) and (it appears) the amp also controls the other units through a "System Control Cord". This appears to be a serial bus (4 conductors) that loops through the units.

The problem is that I wasn't given the cords so nothing appears to work. Where can I get a set of cords? Or can anyone tell me the type and manufacturer of the plugs so I can make up the leads myself?