Fiesta Mk3: help retro-fitting heated front windscreen

I have just had a new windscreen fitted to my Ford Fiesta Mk3 F/1989 Ghia Low Series spec and it happens to be heated. I would like to add the switch to the blanked-off hole in the dash and use it! Of the four gaps I have, the rear heated windscreen and rear fog lights occupy two; same for the front are not present and blanked-off.

I have checked and the relay socket with a mass of wiring to/from it is present though the relay itself is missing. The two 30 amp fuse holders (simply slotted beside the fuse box) and fuses are missing but would be easy to add as would the wiring to/from it. I do not know if the dash switch wiring is present.

Has anyone added a functioning heated front window post-factory to any Mk3? My questions are:

1. Is the wiring/ plug for the dash switch present but tucked away somewhere behind the dash?

2. I cannot see wiring to the windscreen or either side of the two missing fuse carriers. Are they present but tucked away? I watched the screen being fitted and the +ve and -ve terminals are accessible.

3. Where can I buy the Ford heated windscreen dash switch (push button with light), the two fuse holders and the relay?

4. Any other tips?

Thank you