If you search for other radio topics one of them will have the 240sx stock wiring diagram. I forget the website but it will tell you what the wires are based off of your stock harness wiring. I used it when I had radio issues when I bought my vert. Then I couldn't test the radio while it was in my lap because they use the bracket as a ground. It's not very hard to figure out the wiring for the stereo but it helps a whole bunch if you know what wire is what. I am pretty sure this was it
http://www.installdr.com/Insta....html click on the pdf for your year vehicle scroll down.
here is the s13 one the format is pin, what wire it is, in car color, aftermarket adapter wire color. A +12 Volt Ignition Wire Blue RedB Do Not UseC Ground Wire do not connect to this wire, see instructionsD Do Not UseE +12 Volt Battery Wire Red w/ Black Stripe YellowF Right Front Speaker (+) Brown GrayG Left Front Speaker (+) Blue w/ White Stripe WhiteH Power Antenna Turn On BlueI Right Front Speaker (-) Brown w/ White Stripe Gray w/ Black StripeJ Left Front Speaker (-) Blue w/ Yellow Stripe White w/ Black StripeK Right Rear Speaker (+) Blue PurpleL Left Rear Speaker (+) Red GreenM Factory Amp Turn On Lite Green Blue Power Antenna WireN Right Rear Speaker (-) Pink Purple w/ Black StripeO Left Rear Speaker (-) Dark Green Green w/ Black StripeP Do Not Use