Just thought I’d add my two cents to this project. I wanted to do this mod for ages. It annoyed me to look at a blanking plate and also, it’s handy for your passenger to also be able to lock/unlock doors if the driver leaves the car for any reason.
I did some research and with thanks to this thread and also to
@ZeA38VSport , I was able to do it too. I bought a used LHD unlock/lock switch from the USA and purchased a wire harness with pins from the AliExpress linked to above. I managed to source a wiring diagram from my collection of A3 PDFs which was very useful. My car is a facelift, and the other car in this thread that had the mod, was a pre-facelift, so I didn’t know if the pins in the module would be the same.
Luckily they were, and the only noticeable difference I came across whilst doing this mod was that I did not need to code the door module. When I went into the long coding, the bit was already activated on byte 2. So, after connecting the door card back to the module and turning on the ignition, the switch worked straight away.
Wiring diagram shown above. The passenger door unlock switch is referred to as E309 and the door module that controls the folding mirrors and central locking is referred to as the J387. You can see that the four wires from the E309 go to the following:
1) Pin 1 from your new switch is the Earth wire (brown) - I tapped into Earth wire for the LED in the door handle recess.
2) Pin 2 from your new switch connects to pin 28 on the door module block connector.
3) Pin 3 from your switch should tap into the blue/black wire of the electric window switch.
4) Pin 4 from your switch connects to pin 13 of the door module block connector.
Wiring neatly routed with all the existing wiring, and joints all soldered, heat shrink applied, and then cloth loom tape. This picture taken half-way through the final wrapping phase.
Switch worked straight away, no VCDS coding necessary on facelift cars. Just be aware that the switches are different on facelift (white glow light) versus the red glow on PFL.
Also, as already mentioned, I needed to trim some plastic off the connector block (from Ali Express) to allow it to fit into the new unlock switch. I think the block is designed for the passenger side of a LHD car, and I was fitting it to a RHD car. A Stanley knife trimmed it very easily with one slice!
