'79mgb radio installation

I removed my Cassette radio and now want to reinstall it. I have a spiderweb of wires from the back of the radio and 2 dual white/white purple wires from under the dashboard. Also a red in-line fuse wired (connected). A black wire from the dashboard (ground or power wire?).The radio wires are mostly speaker wires (blue,green,grey,black). My MGB Diagram shows a white/green wire to the radio. I can't find it under the dash(?)

Problem solved: Black wire needed to be grounded. Blue wire was only used in case car had a power antenna. Other wires go to individual speakers. Red wire with in-line fuse eventually connected up with the cars' white/green wire for power to the radio.