Auto-dimming (anti-dazzle) mirror retrofit [guide]

[milanj]

Hey guys!
 
Just finished a successful retrofit of auto-dimming rear view mirror today on my Octavia III 1.6 TDI (81 kW, MY2016, ambition) today. So here's a short guide if anyone else decides to do it.
 
 
What you need:
 
1. Auto dimming mirror
You'll need a mirror that supports auto dimming function, VAG code 7N0857511L is the correct mirror for our Octavias, Golf VII, etc.. I managed to get one from eBay. It was used but in very good condition (after cleaning like a new) and I got it for 23 € (L20).
 
2. Harness
You'll need a harness with proper connector, to do all the needed wiring. I got one from AliExpress, for quicker delivery carsystems.pl also has them.
 
 
Wiring:
 
Luckily guys from Golf VII community have already done this mod, so wiring instruction were available. The wiring diagram below is from VWVortex forum, known retroffiter DV52.
 

 
You have to connect 4 wires:

• Black/Yellow wire (switched +12V, terminal 15)
• Brown wire (Earth)
• Black/Blue wire (BCM PIN #64 Socket A - "Right reversing light - M17")
• Brown/Red wire (Interior light connector PIN2)

Black/Blue wire and Brown/Red wire make sure that auto-dimming function doesn't work when interior light is switched on or when you are reversing. 
 
 
Let's do it:
 
I started by first removing old mirror. It's pretty simple. First you remove the plastic behind mirror, which you just pop-off. Make sure to use plastic removal tools, so you don't damage the plastic. They you remove the mirror (inc. bracket) by holding and turning the bracket counter clock wise. Under the mirror, a humidity or rain-light-humidity sensor will reveal itself - you don't need to remove that one further.
 
Then I removed the interior light switch panel. Pretty simple again. First you remove sunglasses holder and plastic covering switch buttons, by unclipping them out carefully. Then you unscrew the two revealed screws (picture below) and continue by pulling the complete panel out (look carefully where it's clipped, so you don't break anything).

 
Now you need to run the wiring harness under the headlining, from mirror to interior light switch panel and then also to the fusebox and BCM compartment of vehicle (on the left side of drivers foot compartment for LHD cars and on the left side of co-drivers foot compartment for RHD). I just pushed between the headlining and windshield, to the A pillar and then down the A pillar to the fusebox compartment. So the wires are now laid out and we need to do the connections..

 

First we connect ground above the interior lights switch panel. There is a screw in place, just waiting to be used as ground.. We connect brown wire to it.

 

Next we need to connect signal from interior lights to the mirror. We take this from interior lights switch panel connector, PIN #2, the blue-brown wire, which we need to connect together with our brown-red wire from mirror to the PIN 2. To do this I made an Y cable, so I didn't need to cut into existing wiring. If you're lacking proper connectors, you may as well cut the wire and then solder them back together...

 

 

 

 

Next we need to move to the foot compartment, to connect our +12V wire and signal from reverse lights.. My first plan was to take +12V from fusebox position 40 (terminal 15) and reverse light signal directly from BCM (socket A, pin 64). When I opened all up and got access to the fusebox and BCM, I decided to find both in the wiring below "dormat" plastic (sorry, don't know proper English phrase for this), to avoid fusebox tampering and due to difficult access to the BCM socket A. So after I removed this  "dormat" plastic cover, I found switched +12V on the blue connector (pictured below), the fat blue red wire on pin 15. Normally I would due an Y wire here, to avoid cutting into the original wire, but lacked proper connectors, so I just carefully removed some of the insulation on the blue-red wire in question, and soldered the black-yellow wire from the harness to it. Looked kinda messy, but it works..

 

Next I just opened up clump of wires laid through the dormat and looked for a black-blue wire, which is the wire that runs through the car to the reverse bulbs.

I found two black-blue wires in this clump and used a 12V tester to see which was the correct one (I hit the right one in first attempt, or maybe both are for reverse bulbs - one for left and other for right one).. I connected the black-blue wire from harness using the same soldering procedure as before for 12V.

 

 

That was it. I fitted back the new mirror and connected it. After successful test I just put all the plastic and everything back to as it was before started, reverse procedure rule..

 

Hint:

You can test the mirror during the day by simply covering the backside sensor of the mirror and it should dim itself. Then, still covering the sensor, you switch on the interior lights and it should un-dim. It should do the same if you put the car in the reverse gear.

 

That's all folks!

Edited 30 August, 2016 by john999boy
Clarification

[john999boy]

Nice write up.
 

[Yoyuuu]

Hello,

 

Does anyone have the electrical diagram for Octavia 2 dimming mirror?

I want to connect exterior mirrors with auto-dimming to the interior mirror which have already rain, light sensor.

 

Thank you. 

[sharkman]

Would anyone know if one of the cables triggers the dimming wing mirrors ??

[effebi]

Hi milanj. Thanks for your tutorial. I'm interested in this mod but, unfortunately, pics you attached are gone. Could you reload them?

Thanks a lot