I have a new harness for the new Stereo System and that is easy enough to figure out which wires go where specially for the new speakers by the given instructions and color coding. The issue I have is the power wires.....looking at the Original Nissan Harness Plugs that are still there but I will not be using and the new Harness and the instructions to attach the red and yellow power supply leads from the new harness to................?? I am looking at the existing harness that is still in the car and trying to figure out........What color wires do I cut and attach to the new harness red and yellow wires power leads?? Anyone know?
Thanks! Mike

1993 Nissan 240 SX Stereo Wiring

Constant 12V+ Red/Black
Switched 12V+ Blue
Ground Chassis
Illumination Red/Blue
Dimmer Red/Yellow
Antenna Left Rear
Front Speakers 4" x 6" Doors
Left Front (+) Blue/White
Left Front (-) Blue/Yellow
Right Front (+) Brown
Right Front (-) Brown/White
Rear Speakers 6 1/2" Rear Deck
Left Rear (+) Red
Left Rear (-) Green
Right Rear (+) Blue
Right Rear (-) Pink

Crutchfield has all the necessary parts and advice for wiring up your SX.

Hope that helps.