Thought I might finally be able to make a considerable contribution to the forum after many years of sucking information from it .
It might even be too late to interest people but I finally got the SWC in my pre-FL wagon to work with the post FL Mcintosh installed.
(Thank you to all those who posted relevant info on this site as none of it was mine. I only had to find the right pieces and put my little jigsaw together.)
I have a pre-facelift Gen IV B-spec. (No SatNav, No cameras, 6MT)
I replaced the PF2551I Mac HU with a PF2824I Mac HU.
I am left with no SWC.
The left A/C knob does nothing and the HU dimmer no longer dims.
It was almost plug-n-play .
The 8 pin i85 plug only had 1 x green wire and the plug body did not fit the PF2824I HU.
The 20 pin i86 plug only had 4 x wires (Brown, Yellow, Blue/white & White) & only the SWC were affected when left unplugged from the old PF2551I HU.
My research found the single green wire fixed my HU light dimming when plugged into pin 2 of i86.
(Sorry about upside down and blurred)
Further on after much trolling on the site, SWC mods were posted and this picture:
(thanks to "m48")
The new HU wiring diagram showed the Orange/white & Purple wires came from pins 3 & 9 of plug i26 and led to the SWC.
I did not have those colours from i26 of my old HU.
So the new HU needed signals to plug i26 pins 3 & 9 (But I couldn't find them).
Other Wiring diagrams showed the Brown & Yellow wires in plug i86 for SWC signals from some strange "LAN" module (What was that suppose to be?)(I had Brown & Yellow, were these the same?).
The picture was of the LAN module.
I found the LAN module and found the missing link to my dilemma.
The Brown & Yellow from my old HU plug was right next to the Orange/white & Purple wires (from the SWC) and all 4 were plugged into the LAN module.
I tested the resistances correctly and (I'm not real bright but) all I had to do was to join the appropriate colours to by-pass the LAN module.
Just move the Brown & Yellow wires from i86 to i26 for the newer HU and BINGO!
I tested the SWC and went and had a well earned drink because I had been trolling for these jigsaw pieces for about 4 years.(not real quick either).
Thx anyhow for anyone that helped in my journey.
Hope this might help someone else upgrade their HU from a pre-FL HU to a post-FL HU.
I have had a good run of it so far with no failures of the newer FL HU.
Cheers