Stereo problems

[cool4door60]

Hi does anyone know any good guides to the wiring behing the stereo in the e30 I have a 1987 318i saloon the stereo was int he glove box unconnected when I bought and thw wiring behind where the stereo goes is a mish mash, I plugged in two different types of stereos the original and a modern unit and both worked fine although it sound like only 3 speakers and it wouldnt switch off via the ignition, I dont know these cars at all as this is my first one, and I am currently without a stereo as its my daily and dont want it running the battery down.

Any advice would help me at this stage?