I've had this mystery for a while, since I bought the car at the start of the year, and one thing and another put off working this part out.

Today I decided to take a look, and as usual took photos and notes so I can pass it on to you good people and for comment.

So firstly, the wire itself is a bit odd. it's a very thin wire, not normal car electrical gauge, i'd say more like low-voltage alarm/bell wire. Secondly it's stripped back, not solder ended or terminated, and with black electrician tape protecting it after the first few cm's.

As they say, a picture paints a thousand words:


So, I took the door pillar plastic apart, at least enough to see what's going on. The plastic is just pop/clipped on, so starting in one corner I prised it open enough to then pop it and clear it a little. For anyone else doing this, pull up the door foot trim pieces of plastic first, as those overlap the plastic housing I was after. It then folds out relatively easily (Watch the rubber door strips).
Behind there I found the wire, wrapped all the way in black tape (almost like black amalgamating tape to be honest), and goes up and into the door switch in the pillar (This is the button for self-closing door). How odd, and it obviously goes nowhere, so it isn't needed. Door button works fine, etc.
Here you can see the two regular wires, plus the strange black coated wire going into the switch bracket:


So I then decided to take the door button out and investigate. The door button pops out also, just prise gently around the edges and it'll come out without too much force. I can then see that it has a 3-pole connector on it which the outer two wires are the regular door button contacts. The middle is this additional wire.

The button itself can also be dis-assembled, this is clipped together so a careful use of screwdriver (Very careful, didn't want to damage this!) prised the switch open, and I managed to take it apart and this is the exploded view of the parts:



I traced the circuit board and could see the three pins that fed in from the back, and could see the central pin looked like had been soldered after-market:



A couple of other things didn't look 'factory' to me too.
That LED had been added, and that black wire (In a R1 position which suggests it should have a resistor there) to bridge the connections.

My conclusion? Somebody has been trying to retro-fit illuminated buttons to the car, so at factory it didn't have the illuminated door button and it's been added. So where that red wire went I suspect must have been to a positive supply from somewhere (maybe tapped into under driver seat, or wiring harness in the floor to the door itself).

Either way, I've removed it now. You may also recall I found similar oddness in my dashboard where it had panel illumination disconnected, and my overhead switches/buttons are illuminated blue instead of the usual green glow, so looks like previous owner was a bit of a modder and was going for an alternative colour scheme! Bit of a cowboy in my opinion, but each to their own!

Hope that helps or at least amuses some of you!

 

Hi Ho Silver...