I would not use an automatic fuse I come across them in my job and they are highly unreliable, also they are not quick acting enough. the fuse is to protect the manual switch if TR2 goes short.
The switch in one position is at 12v, in the other position it is at ground, it is therefore essential that the fuse be quick acting otherwise you will have a burnt out switch.
I agree with your other comments, mine is hard wired and built into a small box.
On the door panel moulding there is a shelf under the mirror/window switch and the box sits nicely on there.
I have had this unit working for 4 weeks now with no problems.
If you are going to build this be careful with the green wire from the central locking, this is at 12v in the unlock position but it is a floating 12v and can not supply much current that is why I have fed it into the base of TR1, the current drawn then is less than 4 micro amps. This wire also comes from the
MICU it is diode protected but never the less be careful you don't stuff 12v up it.
H