Is it possible to retrofit 2003 to heated mirror and puddle lights? Maybe a working harness from a later car? I don't need heated seats here in Ca. But the fog builds up on the mirrors here. I need rear fogs programmed and heated mirrors would be useful.

 

Might want to check and see if you have 5 wires vs. 3 on the body side mirror connector. They would both be black. If you do, you'd only need the mirror side w/wires and terminations on the mirror. Can't see MINI making an entirely different harness just for heated mirrors.
Puddle lights can be added - there's an OEM option, IIRC. But it's not plug and play. You've got to drill holes and run wiring.

 

I just did a puddle light upgrade on my 05/2003 R53 Cooper S.. No need to drill anything, just cut some rubber grommets. Did both doors! Looks great.

https://www.northamericanmotoring.co...r-the-r53.html

Can't help you with the heated mirrors, I think that needs a different electronical control system.

 

Heated mirrors is easy, just feed them off a switched feed, no fancy controller.
Buy a heated mirror, swap with unheated, run ground to door metal.
Then run feed through existing car to door route, get switched feed from fusebox in footwell.
Simples.........