Ello,
Bought my mrs a 2006 FL, leather interior, I noticed the seats had wiring that fed towards the dash but no switches so I bought the switches and bingo heated seats work, now at the same time I pulled out the blank heated from screen switch which also has a plug and wires, would it be so simple just to change the non heated screen for a heated version? Where would the wires for the glass be located? Any help appreciated..

No heavy wires are there, nether is the standard alone fuse box for the heated front screen. I suspect you'll also need to tell the CCU that the HFS is fitted, and get the screen installed, which is far from cheap.

I looked into this conversion when I was looking for my current FL1. After much research and pricing up, I decided it was better to find a vehicle that was already fitted with the HFS, so rejected any FL1 that was missing it.