Do anybody know what thread the Switch for oil pressure, type PRC6387 Lucas have?
(think someone installed a M10 helical thread in the oil filter holder and now the original switch don´t fit.....) Guess I need an adapter of some kind.
Grateful for any advice!

Info I have added to manual.
Oil pressure sender thread 3/8"BSF early imperial engine
M10x1.0 Metric engine.

The oil pressure switch for the metric 2.5 engine is PRC6387 but I can only presume it has a metric thread.
Edit. I found a PRC6387 in my spares along with a T piece. The switch screws into the T piece which gives me doubts about a metric thread on it.
I don't know whether anyone could tell what the thread is if I took a photo.

The correct switch is GPS102 according to the Series 2A parts list and Blanchard's have them in stock at £3.20 plus VAT and carriage. Is that the switch you're trying to fit?
I don't think PRC6387 is metric but probably has a different thread from the correct switch GP102.

Thanks for prompt response!
I´ll order a new switch GPS102 and give that a try, the thread in the holder seems to be M10,
and as mentioned this might not be original as I think a tread repair "helicoil" have been installed to repair damaged threads. the GPS102 seems to have 3/8" thread so maybe I still need an adapter.....if such M10/3/8") exist.

If yours has been tapped to M10x1.0 just get a later switch. They're only to turn the light on and not 'calibrated' like a sender for a gauge would be. One from a Tdi would fit an M10x1.0 hole. No adapter is one less place to leak from.

I'm convinced that PRC6387 isn't metric because it screws into the T piece and that isn't metric. This switch is for TDI engines as well.

If Craddocks is correct PRC6387  is for ALL 4 cylinder vehicles up to 1998, I am certain that would be 3/8 " Pic of an original  NOS Smiths

thanks again, looks like I'll be in the market for a M10 to 3/8 adapter......if such exist.

Are you absolutely sure the thread is M10? I can't imagine the filter holder being helicoiled. Surely there'd be swarf and that wouldn't be easy to remove.

Quote from: Alan Drover on Oct 07, 2024, 11:34 AMI'm convinced that PRC6387 isn't metric because it screws into the T piece and that isn't metric. This switch is for TDI engines as well.

How odd. My 200tdi is certainly M10x1.0 because I remember checking to make an adapter to feed a gauge as well as the light. Maybe mine has already been messed with?

I've replaced the switch on my 2.5 petrol ages ago. I think I got it from Craddock's but I can't remember when.
My spare PRC6387 is a Britpart. I'll dig it out tomorrow and photograph it trying to get a clear view of the threaded part.

This is my PRC6387. Now, idiot brain here thought it screwed into the T Piece. Well, it DOESN'T. I didn't screw it in far enough and it only goes in for the first couple of threads so it must be a metric thread.
It fits engines that have the spin on filter, the ones with the replaceable element take 90519864 which equates to GPS102.
Apologies for any confusion. My stupidity has messed up my plan to fit an oil pressure gauge. I've now got to find a suitable metric T piece.

Thanks all for your efforts.
My latest thoughts are to look for an alternative switch with M10 treads, as this isn´t for a sophisticated gauge more an indicator light. Question is of coarse what pressure it should indicate.....when the light goes on? Can that be read on any of the switches?

Typically oil pressure switches come "on" at around 10 psi.