Hey Guest!
smilie in place of the real @
Pretty Please - add it to our Events forum(s) and add to the calendar! >> Here's How << 
It is arguably easier to purchase the proper escutcheon, part number 611974, which has space and other provision for the correct OD switch. Readily available from all the usual suspects! Of course, this advice applies only to the TR4A and later, as Geo suggests.I did this on a TR4 -- just ran the wires down the same 'dagger' as used for the turn signals, etc. That area may be a bit more crowded on a 4A if (as I think) the headlight switch is on the column and uses that same route.
I had to add a D-shaped hole in the right side nacelle, maybe you will too.
I think the plastic/metal cutover point was right at the 4/4A change. On the 4A the switch is on the left side, doubled up with the turn signal switch.
Hey Tom... welcome back by the way!
Since don can't find his D-drill, you might consider going to a square drill bit. Yes, I can supply one if needed....