The wiring that you're referring to is the link lead kit for later cars.
LINK KIT YMZ000120 FROM VIN 24554 TO 03MY279844
YMZ000150 FROM VIN 279884
It's used in conjunction with the original MGR tow bar wiring kit
Rimmers have YMZ000150 in stock
The fitting instructions are on Rave in the acessory section, I don't have access to my laptop at the moment so aren't able to advise how it's fitted but here's a thread on here that may help.
https://www.the75andztclub.co.uk/for...ad.php?t=23041
Funnily enough you posted on it in 2013
Russ