The switch in the body as best I am aware is NLA,
While we're on this subject can someone enlighten me as to the difference between the black AAU1752A the switch which is NLA and the white AAU2454 and AAU3821A switches fitted to many other classics including MGB.
Is it the metric vs UNF thread thing again?
There's an article here, but it doesn't explain the difference
https://www.moke.com...e-fail-switches
The two switches were used with different shuttles in the (in built) PDWA Valve.
The original type fitted to a Mini was a true (press) switch. The 'button' on them was held in by the PDWA Shuttle when in a healthy mode, but would release and lock the PDWA Valve on a pressure differential in the system.When repaired and bleed, the Switch needed to be removed, the pedal pressed hard to re-set the Valve Shuttle, though, more often than not, they needed help. I found them very unreliable.
The White 'Switch' was in fact, just a contact, it's not a switch at all. These worked with a different shaped Shuttle in the PDWA Valve. The Pins in them are on a common contact on the threaded end. When screwed in, it was in 'free space' but in a fail mode, the shuttle would move and touch the contact in the body of the 'Switch', making the circuit by Earthing it and bringing the Fail Lamp on. Best I can tell, this was a cost cutting exercise.
The way the Fail Lamps were wired up in our (Australian) Minis and Mokes, these two switch types can't readily be interchanged without wiring modifications.