I'd start from one side of the circular plug and use that as a starting point. It is probably the second option I just gave as alot of systems back then had a shared ground type of setup, which would be from the deck ti the amp, then your typical left+&- and right+&- out to speakers. Either that way, or the reverse of what I just said, with 4 wires going to your speakers(left+,left-,right+,right-) and the other 3 wires are your input from the deck(left+,right+ and common ground).
With 7 wires, I'd bet that 4 of them are your input(left and right+ and left and right -) and the other 3 go to your speakers(left+, right+ and a shared ground). How is the eq part hooked to the amp? Is it connected internally and not detachable? I tried googling some stuff and came up with nadda.
