1990 Toyota Supra Stereo Wiring (some of these colours are the same for other MKIII Supras, others are not, contact me if you have a specific question)

There are two plugs that connect to the stock stereo and these are shown below (from these drawings you can see why I'm a Telecomms Consultant and not a CAD operator)

Plug A
Pin 1 - Light Green - Front Left Speaker
Pin 2 - Purple - Front Right Speaker
Pin 3 - Grey - Accessory Power (i.e. on when key is turned to ACC)
Pin 4 - Blue and Yellow - Permanent Power
Pin 5 - Blue - Front Left Speaker
Pin 6 - Violet - Front Right Speaker
Pin 7 - Brown - Earth
Pin 8 - Black and Red - Antenna Control Relay (unsure of purpose)
Pin 9 - Pink and Blue (lovely) - Antenna Control Relay (unsure of purpose)

Plug B
Pin 1 - Red - Rear Right Speaker
Pin 2 - Black - Rear Left Speaker
Pin 3 - White - Rear Right Speaker
(No wire on pins 4 or 5)
Pin 6 - Yellow - Rear Left Speaker