See below. A switch on the bolster of the drivers footwell.
I'm assuming its something aftermarket fitted by a PO?
Can't find anything in the owners handbook

Anybody know what it is?

Click image to enlarge

I found this same switch on my 3.6 when it was delivered brand new. I wrote a post on here about it fifteen years ago!

https://www.fullfatrr.com/forum/topic943.html

I was told it was a thing for the dealers to access electrics without using the key. Apparently, it normally gets disconnected at PDI, but is often overlooked! The older I get, the more I realise that people confuse wrinkles for wisdom

Thanks JMC, very interesting....
Mine is disconnected as it doesn't seem to do anything..
Like a poster said in the original thread, no wonder RR's are easy to steal if they left some of these connected by mistake All the best
Chris