I have an old Pioneer KEH-8080B radio cassette that I am trying to fit
to my motorcycle.

The problem is the wiring to the speakers.

I have connected all the power OK but have only got green, green with
black tracer, grey, grey with black tracer to connect to four speakers.
I believe the grey is the front left and green is the front right.
Where do I connect the other terminal on the speaker?

Any help gratefully received.