Fitting lucas style door mirrors

[AndyPandy]

Remove the triangular cover at the bottom of the quarter light. Carefully mark in pencil the width of the door frame on the front and bottom of the cover.
Having removed the cover you will see where the window rubber seal ends, again mark this onto the cover, you will then see the area that you can drill the appropriate hole, remember to drill the hole only through the outer side of the cover.
Having drilled the hole , Open the quarter light as far as it will go and gently pull out the rubber seal from the bottom curved corner.
After drilling the hole replace the cover you will then be able to see how much you will have to shorten the mirror arm screw in order to be able to fit plain washer lock washer and nut.
It is just a bit awkward fitting the washers and tightening the nut but it makes for a much neater finished job. And no need to have grommets on show on the interior.
Having tightened the nut, and the arm set in the correct position then carefully refit the rubber seal close quarter light fit mirror head and adjust as required.
Repeat if fitting mirror to nearside door.
Hope this proves helpful :

[MarkyB]

Maybe I'm being slow but I don't understand this part "Carefully mark in pencil the width of the door frame on the front and bottom of the cover."
Surely there isn't a bottom on the cover.

[AndyPandy]

The door frame on the leading edge of the door and the bottom frame that the cover screws onto .Both are about 5/8 square. By marking the width of these along with the rubber seal position onto the outer side of the cover in pencil it allows you to position the plain washer for marking off the hole.