(Updated)
Having looked around for info re replacing a standard mirror and an auto-dimming rear view mirror, I have found this and other posts useful. The following details my own experience with a 2006 A6 C6/4F. It seems quite difficult to find out what part code you need (mine has a light grey trim), so all I can say is get something that looks right, and pay particular attention to the bayonet mounting onto the windscreen.
This is my old mirror, the windscreen mount, and the common bayonet mount:
This is the new mirror that I found on eBay for £33 which was in excellent condition. It was from an A4 B7 (2005-2007) donor car - Auto Dimming Rear View Mirror - 4F0 857 511 E 1YE.
The wiring to the mirror is from a 6 pin connector. This post already details the pin number and functionality, but does not state that the pin numbers (and where pin 1 is located) are clearly visible on the connector itself.
For completeness, the pinout and colours are as follows:
- Pin 1 (White) - 12v (connect to ignition, or even better when lights are switched on).
- Pin 2 (Black) - Ground.
- Pin 3 (Grey) - No connect (says to wing mirrors - but looked low when not connected).
- Pin 4 (Yellow) - No connect (says reverse signal - but looked low when not connected).
- Pin 5 (Brown) - No connect (says to wing mirrors - but looked low when not connected).
- Pin 6 (Green) - Active Low (connect to interior light switch, low it prevents dimming, float high allows dimming.
Measuring the operation of the mirror on the bench, the power requirements of 'my' mirror were as follows:
- - 210mA (peaks at 300mA) @ 12v to dim (with green and power lights on),
- - 100mA when switched off (green power light off).
- - 107mA when not dimming (green power light on).
- - 112mA when not dimming because pin 6 is inhibiting dimming.
So when installing the mirror it is essential that no power goes to the mirror when the ignition is off (else you will get a flat battery very quickly).
I decided (as recommended in posts above) to use wires: power, ground, inhibit (pins 1,2, and 6) and so found some wire (black, red, orange) and a spare PC fan extender cable. I removed the connector from the mirror and soldered on the male half of the PC fan connector onto the three wires I was using, and isolated the remaining wires on the mirror (and stuffed them back into the mirror). The other half of the PC fan connector was then soldered onto my black/red/orange wires. This would allow me to fully disconnect the mirror i.e. in case of windscreen replacement. I added wires that were 75cm in length thinking that I would cut them down during installation, in fact after routing and securing the wires, 75cm was only just long enough.
My intention was to power the mirror from the interior light fitting. This fitting is removed by gently pulling off the covers, which then expose 2 posi-drive screws (towards the windscreen). Once the screws have been removed then the whole thing unclips and will dangle on the wires. In this state it is very easy to route the new wires under the front of the lining, towards the existing loom. Sorry I don't have any pictures, but it is really easy/obvious.
Next task was to wire it in. After some experimentation, I decided to tap off the power to the red LEDs that light whenever the sidelights/headlights are on. Power is sunk through the LEDs and through a current limiting resistor, so this was ideal (and it was easy to get to). My car also has auto-lights, and I could not think of a reason as to why I would ever want the mirror to dim when the lights were off. I also decided to connect the inhibit line (pin 6) to the high side of the interior light. On my car I found that when the light is off, one side of the main bulbs sees a high (after the bulb, approx .10v) but when the light is on, I assume a FET turns on and sinks current to give effectively 0v. This means that when its dark (mirror dimming) and the interior light is switched on, the mirror will un-dim so you can see what's behind you properly.
This is the top view of the interior light unit, next to the mirror:
The green circles show the two screws positions that secure the unit in place. The yellow circles show the red LEDs circuit that I tapped into to supply power (when side light are on) and ground. The LED circuit connects to the unit with spade connectors (red circles) Underneath the spade is a small hole - so to make the connection, I just partially removed the spade, pushed my black/red wires through the appropriate hole, and pushed the spade connector back on - trapping my new wires. No soldering, no altering anything, very secure. I did a similar thing with my orange wire, just pushed out the bulb holder a little, pushed the orange wire in and pushed the holder back in to secure the wire (not ideal, but more than adequate). I then used some cable ties just to make sure nothing could move in the future. Replaced everything, job done.
When the side lights come on, the auto-dim is enabled and operates, The mirror's green LED is illuminated. The button can be used to switch off the mirror, but next time the lights are switched on, the mirror will be enabled again automatically. The auto-dimming then operates as expected, except when it's dark and the interior light is switched on (causing dimming to be inhibited).
I hope that this information is useful to at least one person! Thanks to previous contributors on this topic, appreciate it.
