the 1990 wiring diagram say:

right rear speaker - BG and BU
right front speaker - BN and BW
left front speaker - BK and BR
left rear speaker - BO and BY

ignition fed live via fuse - WO
from fuse A3 illumination from LH sidelamp circuit - RB
from fuse B2 constant live - PW
earth - B

colours:

Black Green blUe browN White pinK Red Orange Yellow Purple

1989 diagram seems to say the same.  You look to be missing 2 speaker wires
and I don't know what the yellow/black does.  There's an input marked from
an aerial amplifier, but I'd have thought that was co-ax.  It uses the
heated rear screen element as an aerial, hence the amp.  If it's not got a
co-ax aerial input, then it might be that the yellow/black is your
connection to the aerial amp.