Can anyone help with wiring diagram for a Volvo CR-702 radio cassette?

Hi Guys
Recently bought a 1990 740 (Base model) without radio/cassette. So I
bought an original CR-702 off ebay figuring I could plug it right into
the electrical connections in the car.
HOWEVER, the previous owner must have wired in a non-Volvo radio and
speakers because I can see non-standard (afterfit) wires which they had
wired into the original Volvo connection block coming out of the car's
dashboard.
So, I can plug the stereo into the 10 pin connection box coming out of
the dashboard and the sterop comes on OK -but I get no sound. I know
the speakers work because I tried them with a portable radio.

So, I can't figure out which wires are the speaker output wires from
the unit. Can anyone help? The wires coming out of the back of the
stereo are:

Going to a black connection box with 10 pins:
Red with thin white line
Grey and thin red line
Blue
1 black one thicker than all the others
Yellow with thin black line
Yellow with thin white line
green with thin brown line
3 blacks with red rings, one of which goes to a separate 2 point
connector
2 reds with black rings, one of which goes to the separate 2 point
connector

The other confusing thing is there is a DIN male plug coming out of the
car innards which I understand is used to take output from the radio to
an extra amplifier of graphic equaliser. But the car does not have
these nor do I think it ever had them.

If anyone can help, I'd really appreciate it. I am trying to get the
740 back to original spec and don't want to wire in a non-Volvo unit if
I can help it.
Thanks in advance.
Pete