First step was to remove the starter. In order to not have to remove the left engine cover and starter clutch, I split the starter at the planetary gearbox
And this is why: So you get access to the casting-mark that goes to the main oil-gallery.
Prior to drilling you either remove the right engine cover or just the oil-filter cover. As the latter is very tight on my TR1, I prefer to take off the complete cover.
Close-up on the filter housing.
As I was admittedly a bit nervous of not drilling perfectly perpendicular, I quickly knocked up a drilling guide. The same goes for the tapping guide. I tapped it in M10x1 as this is a standard thread for oil-pressure switches in Continental Europe and can be found on many German vehicles.
If you read this and are from the US or UK, you may want to check your local parts store for a roughly 1 bar, opener switch.
I decided to drill the hole undersized by 0.4mm as I used a handheld drill.
Tapping in progress.
And where you end up inside the filter housing.
Oilpressure switch in place.
This is the original oil-level sender unit. I chopped off the cable and then extended it a bit to run it up to the new oilpressure-switch.
Another thing that totally made sense was to clean up the starter from carbon deposits.
Recommended oil-pressure switch:
Hella 6ZL 003 259-437, 1bar, opener