Much more to auto lights that the switch. Your rear-view mirror needs to be replaced with a model with a built in sensor and your windshield / windscreen 'may' need to be replaced as well.

You will need to build your own wiring harness as Audi is notorious for only pulling wires for the options purchased when new (so don't expect to plug-in options after the fact).

It can be done with enough patience and money. A search using the search tool at the top of the page should bring up details on what all's involved.

Here is one written by MT-V6 to get you started:

Retrofit: Auto Headlights / Wipers / Anti-Dazzle Mirror

I have just finished retrofitting automatic headlights and wipers as well as the auto-dimming rear view mirror. I had these options in my last car and it's something I missed. It took a fair amount of research in order to make up all the wires needed, but overall I think it was worth the effort...

www.ttforum.co.uk

 

Thanks. Yeah much more work compared to how much I want auto lights!
There are a couple of sensors (blank housing?) on the dash, I read one is a light sensor, do you know what is this for?

 

(A) G107 - Sunlight Photo sensor linked to the Climatronic system. The system needs to adjust the fan speed and temp flap to maintain the temp set on the display. With more sunlight it assumes, for example, more cold air is required to maintain the temp set on the display.
(B) K133 - Alarm LED
FYI - There's another light sensor built into the instrument pod (arrow) which controls the dash lights. You'll notice this working if you have your DLR on and you go through a tunnel; the gauges dim out, but the needles remain illuminated.