To Retrofit the Oval mirror to a car that came with a square mirror with assist, clown nose, and auto dimming:
1) On the mirror side of the plug push out pins 4, 5, 6 and 7.
2) Pins 4 and 5 are connected together by a white wire, Pins 6 and 7 are connected together by a green wire.
3) On the mirror side I cut the white and green wire. You can fold them and put them inside the neck, or you can just tuck the wires out of the way without cutting them.
In my case I thought this was merely plug and play and found out this was not the case. My mirror popped and then smoke poured out of it. Not a good sign...
Anyway, I found the following info which also helped me to get my Oval mirror to finally work with my BMW Assist M3...
M3 with Assist wiring is similar but different from other E46 vehicles:
M3 Car connector located near rain sensor, no homelink (10 pin connector)
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Pin 1 +12V when car is put in reverse, I believe so Auto Dimming is disabled while
Pin 2 -BLANK- NO CONNECTION
Pin 3 +12V Ignition source (Power Auto Dimming circuitry)
Pin 4 +12V Constant source (I-Bus for Assist)
Pin 5 Parking light +1.5V (used to light the Assist buttons)
Pin 6 ?????
Pin 7 +12V Constant source (Power "reciever" for remotes)
Pin 8 +12V Constant source
Pin 9 LED cathode (-) This is the clown nose LED
Pin 10 Ground
Please use this information as a guide and verify your pins/connectors before installing any mirror.
The '03 oval mirror wires correspond to the following pins: (this matched my '04 mirror)
Pin 1 Black
Pin 2 Red
Pin 3 Yellow
Pin 4 White
Pin 5 Green
Pin 6 White
Pin 7 Green
Pin 8 Purple
Pin 9 Blue
Pin 10 Brown
Hope this helps you out! The information is put out for your reference only.......just be aware of this and verify for your car......
I performed the modifications as mentioned above for my M3 and took a drive the evening I installed my retrofitted Oval rear view mirror. Everything worked on my modded mirror. No smoke or abnormal indication. No automatic dialing of BMW assist either. As far as anyone would know this mirror came with my car.