On an after market radio (Pioneer, Alpine, Sony, Kenwood, etc.)
Red = ignition (switched power)
yellow = battery (constant power for memory and internal amplifier when on)
black = ground (bolt it to the bolts on the tranni hump)
Blue = external amp remote wire
Blue/white = antenna remote wire
Orange = dimmer wire (connect to dash lights to dim radio apon turning on dash lights).
Pink = cell phone mute (for hands free kits, mutes radio when cellular signal is detected.
White = front left speaker (+)
White/black stripe = front left speaker (-)
Grey = front right speaker (+)
Grey/black stripe = front right speaker (-)
Green = rear left speaker (+)
Green/Black stripe = rear left speaker (-)
Purple = rear right speaker (+)
Purple/black stripe = Rear right speaker (-)
If you plan on installing an aftermarket radio into a 240Z, none of the stock wires really matter except the one from the ignition (accessory position). Run a wire from a solid constant (white/red stripe on ignition)
The antenna switch will not fit next to a DIN sized radio (DIN = 2" x 7") it'll work with a 2 pole radio. Picture below will show that here's no room for the stock antenna switch. There are aftermarket antenna's available that work great in the stock location. The Metra PW-22 fits beautifully, I have one. Pictured below. Just hook up the blue antenna wire to the blue wire on the PW-22 and it works great.
Invest in a decent test light, test twice, connect once.
Hope this helps a little.
Dave.