Internal mirror wiring for dimming mirror

[pete-p]

A while back now I bought an auto-dimming internal mirror but due to various reason I am yet to try and fit it!

I am hoping that I can splice into the mirror loom rather than using the wiring in the car, that way if I or someone else ever wanted to change back it will be simple.

As I have a facelift car with the ambient lighting I was thinking tapping into that would make the most sense as it would then activate with the headlights, what I haven't been able to find is which wires this would be. Does anyone know which these would be?

I came across the picture below from Goran when fitting his dashcam which shows the reading lights circuit. in this post http://forum.a8parts.co.uk/showthread.php?t=11184

This leaves the Green/Cream, Grey and Blue wires to check.

[HPsauce]

Racking my brains a bit on this, I fitted one to my PF S8 which has rather less wiring up there!
The best place I found to wire in was the sunroof circuit, easy to identify from the switches on PF.

That circuit (checked by testing with a multimeter and I'd guess FL is the same) is live with ignition on and goes off after a small delay when ignition is turned off.
It obviously doesn't matter if it's "active" when the headlights are not.

[steamship]

This is the thread that I referred to when I fitted mine:

http://forum.a8parts.co.uk/showthread.php?t=1100

[pete-p]

Thanks for the replies. I think I've read almost all there is about the wiring there but was really hoping I could use the feed for the ambient lighting and connect it all in the one harness before fitting it in.

I may dig out my multimeter and see what the blue and grey wires do, perhaps that's where I need to look first. I saw mention of blue with red stripe being illumination so there could be a link there with the plain blue in the mirror harness... probably too simple though!

[MikkiJayne]

Didn't we have a thread on this recently where we decided it's possible to do it with four of the six wires on the mirror, just using things that are in there already? If I recall correctly, the only things which aren't there are the reverse signal (to disable the dimming) and the output to the door mirrors (which aren't there anyway).

[pete-p]

That might have been me in the sale thread

http://forum.a8parts.co.uk/showthread.php?t=15718

I'm sure it's possible, just need to identify which of the three remaining wires to use.

[steamship]

Just to confuse you even more. I knew I'd posted about this before but couldn't remember when and couldn't find it last night. Finally found it:

http://forum.a8parts.co.uk/showthread.php?t=12806

[pete-p]

Thanks Sean. I read your post there and it was very helpful as mine has the same coloured wires as yours.

One thing I see from that and which probably ties in with what Andrew noticed, there is a feed to the dimmer from the interior lights. I wonder if this is to cancel the dimming when the interior lights come on? Could be handy to connect this one up to make it easier when dropping someone off!

[HPsauce]

Originally Posted by pete-p

I wonder if this is to cancel the dimming when the interior lights come on?

That's the sort of clever feature that you'd expect on an '8!
Though personally I'd probably avoid using that input unless you're doing a full OEM install - you just never know how the various controllers interact so KISS.

I also note from that thread Sean took power from the sunroof (as I did on my PF) and similarly just found a good earth point.

[pete-p]

So I've been studying the wiring diagram for the interior lights and think I have the solution.

The usual plug on the mirror with/without dimming has the pins below:

1. Red - Always live even when ignition off.

2. Grey/Green - Switched live with headlights. Also same colour wire provides power to other lights (e.g. ashtray)

3. Green - Unsure. Some reversible ground from lights? Goran indicates this as being activated by driver's reading light switch but then connected it to the negative for the Dashcam.

4. Grey - Not sure but possibly related to headlights or perhaps the other reading light, only other grey I can see is between the headlight switch and the relay in the footwell.

5. Blue - Ground. Another blue on the tiptronic switch is connected to ground (brown) so seems logical this does too.


So I found a 9v battery and connected the positive to pin 2 and negative to pin 5 and the red ambient lights switched on. I think this is where I need to connect pins 2 and 1 from the dimming circuit.

Not sure if I can connect pin 3 from the mirror (linked to reading light switching) to pin 6 of the dimming (normally connected to interior front and reading lights) any thoughts?!