The 1993 BMW 325 radio wiring colors are red, brown, green, yellow, and white. The red wire is the positive wire. The brown wire is the ground wire. The green and yellow wires are the speaker wires. The white wire is the auxiliary wire.
http://www.modifiedlife.com/1993-pontiac-bonneville-car-stereo-wiring-schematic/
Visit www.InstallDoctor.com. you can also save yourself a lot of misery by just spending $10 on a stereo wiring harness made for your vehical... save a lot of time. its for replacing the tired radio for a newer sound system..
autozone.com try www.autozone or the website of the manu. of the CD player
It looks like color coded spaghetti.
www.installdr.com/Harnesses/Ford-Wiring.pdf
The best idea is to purchase a wiring harness adapter, these are readily available on eBay for around $20.
NEED COLOR CODE FOR RADIO SPEAKER WIRE 93 MERCURY
electrical wiring diagram
1993 Jeep Cherokee Ignition Wiring ...
Most repair manuals have the wiring diagrams in them.
I'm not sure on a "schematic" but here's the wiring info and color coordinations: http://www.the12volt.com/installbay/stereodetail/931.html
prob the best source would be a haynes manual. it has the best schematics and step bt step repair i have seen.