Preparing the new mirror
I used a long self-tapping screw to fix the BMW ball to the end of Nissan mount. The BMW ball already has a hole through it so just drill a pilot hole into the Nissan mount and screw together. The resulting bracket should look like this:
To wire the mirror up I joined a length of black 2-core power cable to the Red (+12v) and Brown (GND) BMW cables. Note: In the BMW the grey cable is also used to input a reverse signal. This is to prevent the mirror from dimming when reversing. I chose not to use this option as I did not think it worth the extra work. I may chose to wire it in the future but could also just fit a switch to cut the 12v power instead.
There is a small round plug in the back of the BMW mirror than covers the tension adjustment. Rather than drill a hole to pass the cable through, I used this hole instead.
At this point I tested my connections by wiring the mirror into a 12v supply. With the power on, cover the light sensor on the back of the mirror and you should see the mirror slowly darken. With this tested, press the mirror and front bezel in place.
The mirror is now ready for refitting:
