Ok I can finally bring an end to this,
@Pauly sent me the wires terminated with the crimped terminal I needed, along with the correct plug to go into the back of the locking switch, and I had a day free so got stuck into it. I already had the door card off so was able to quickly attach the connections for switch illumination and ground, both available on the back of the mirror adjustment switch, and fed the remaining connector through the door wiring "tunnel" to below the steering wheel. The lower black trim has a couple of torx screws holding it then just unclips, and the trim on the lower half of the dash just pulls off. I also removed the shroud round the bottom of the steering column to give myself a bit more room.
Once upside down in the footwell you can see the two 73 pin connectors that go into the back of the BCM and they can be unplugged without removing the BCM itself by hinging up the white clips and pulling horizontally towards the front of the car
(the flat side on the left goes into the BCM). To help distinguish them, one is white and one is black (I wanted the black one 73A), and pushing in a little clip either side allows you to slide the connector block out of the hinged surround. Once you do, you separate the connector block into two halves by holding the sides and sliding in opposite directions
Once you've done this you can see that each pin is numbered (they're very small but they're there) and once I'd found the pin I needed (25) I found that I couldn't put the crimped connector in as there was already a yellow wire in it. After further consulting with
@Pauly he confirmed that was ok and to attach the wire to that yellow. That did prove difficult as it was in the middle of a thick bunch of tightly wrapped wires heading up the dash with hardly any slack, but after just a faint whiff of burning floor mat (oops) I had the connection soldered and heatshrunk. After reassembling the connector and plugging them both back into the BCM it was time to re-connect the battery and hold my breath and ... Success!
I really find putting the lower trim panel that fits round the light switch surround difficult and it took a lot of bending (and butchering the plastic round the surround itself, which is thankfully hidden when assembled) to get it back on, but with all reassembled it works perfectly and is indistinguishable from factory
And yes I know the door card isn't back on properly, I can never get that right first time.
Boosted by the achievement, I then ran the cable for my rear dash cam and installed it, also running the rear cable for my upcoming 360 cam project, plus a spare 12v supply to the back while I had the trim off. All in all a good day, in fact I feel epic! Where's my high heels and hot pants
Huge thanks again to
@Pauly for all the help, it's an unnerving experience pulling apart a 3 month old van and making new connections to the BCM and he gave me the confidence to give it a go
If anyone ever needs to do this, or you've come across this on a Google search, get in touch and I can give you any more details you need.
