One of the most obvious differences was the shape of the plug that connected to widow motor. 318is was square type and the M3 was oval WTF. There were more plugs going to the door handle on the old loom too.
It baffles the hell out of me.
Look at number 24 on both of these... http://www.bimmerforums.co.uk/forum/...wreply&p=40677 http://www.realoem.com/bmw/showparts...g=51&fg=10they list the same but they were totally different. This is the only time that i've found a discrepancy whilst using realoem (perhaps my coupe was a Friday night car)