3 litre brake light switch

[djm16]

I understand there were two different brake light switches, the change occurring with the Mk IIC. Early switches being 1/8 NPT and later ones 3/8 X24 UNF.
Is this correct?
And if I have chassis number 74100066A, does that make me a Mk IIA?

So what switch do I need for mine? I do not trust that the one that came out is the correct one! I suspect the 1/8 NPT.

[Phil Nottingham]

A very early Mk2c then - the UNF is the later type and needs a sealing washer as its got a parallel thread. The NPT are taper thread. The NPT will screw into the UNF T Piece and seal if it does not split the union. The UNF one will also screw in to the NPT T piece but will not seal

[djm16]

Hi Phil,
Thanks for replying.
Do you say it is a IIC on the basis of the chassis number? The only info I have is that 741 indicated export, RHD, auto, and the series started at 1A.

If it helps it has Layback seats.