HU wiring

I've got an old philips hu from a nissan, not sure of the year but its one of the old black ones comonly found in older pintaras/camrys etc. At a guess i would say 88 - 90 for the year. the label reads NISSAN 28010 J7502 PHILIPS DC 568/69 12 VOLT NEGATIVE EARTH SPEAKERS 4 OHM MADE IN SINGAPORE Sv0749 005240 I've had a google and couldnt find wiring schematics, it has: red fused (+12v) grey/black, thicker then the other wires (-12v?) green grey white If anyone knows which wire does what it would be greatly appreciated :)

definitely sounds as if it uses a common ground for the speaker output wires it wouldnt be -12V.. it may be ground

Forgot to add in the first post, the grey/black is a straight connection to ground. It does look as though there is a common ground for the speakers, a little later on ill get out a crappy old speaker and have a go at trying to find the connections.

Got the wiring worked out, i accidentally not paying attention hooked the +12v alligator clip to the white wire and spent a few minutes trying to figure out why it wouldnt turn on. RED          +12v GREY/BLACK     SPKR GRND WHITE          +Clock GREEN          +LEFT GREY          +RIGHT