Hi Folks
Just had the windscreen replaced - and they fitted a heated screen even through the old one was not heated - had to take what they had in stock.
My question is - if I wanted to make a homemade power supply to it - is it as simple is just supplying 12V to the connectors and a timer switch to the power supply?
Any advice would be greatly appreciated.

I would think it possible to retrofit the HFS. You should find most of the wiring is already there. You would simply need to add the fuses/relays and the correct HVAC control panel, and then activate it in the CCFs. Hyundai Ioniq 5 Ultimate. The family car.
2009 Rimini Red SE TD4. Gone.
2006 Tonga Green i6 HSE. Gone.
Audi A5 convertible, my daily driver.
1972 Hillman Avenger GT, the project.

I considered fitting a HFS when I needed to replace my screen but was told by a member on here that the wiring was not already in place. (So I didn't bother). Landrover - turning owners into mechanics since 1948

2014 Orkney grey Freelander SD4 GS.
2004 Zambezi silver Discovery 2 Td5 (Gone)
1963 Surf blue Morris Mini Minor Super de Luxe (my little toy)

I know they fit heated front screens in many race saloons/rally/competition cars as they normally have the heating system removed. Why don’t you check out those sites as they may do a relay/timer kit that might work for you? Past: FL2 TD4 HSE Auto
Evoque SD4 Dynamic Lux Auto
Present: Audi A3 S Line.

The commonly available Defender heated screen kit would do the job, would check under the plastic scuttle first though to see if you already have the wiring? The post 2012 facelift models certainly already have the wiring in place