Following a search I have found the original installation manual. I am
posting the information in case it is usefull to anyone else.

Connections are as follows:-

red To electric terminal controlled by ignition switch (12v DC)
ON/OFF
orange To terminal always supplied with power regardless of
ignition switch position
yellow To lighting switch terminal
black Ground
blue To auto-antenna power terminal (Max 300ma 12v DC)
green Left speaker front
green/black Left speaker front
grey Right speaker front
grey/black Right speaker front

Rear speakers are from the din plug connection through a seperate power
amp.