Thanks gtogreen. The light goes out when the wire is disconnected, so it does sound like the switch is the culprit. Is it replaceable? It looked like it was integral to the filter head. I took the filter head off and the bypass appears to function (the ball moves freely).

Hi 68+68, there isn't a pressure light on my car; it has the bypass light and the oil pressure gauge on the dash.

If the switch is integral to the filter head then all I can suggest is give it a good clean in the parts bath. A few taps on the bench and maybe some air pressure in different holes. You should be able to test the switch is open or closed with an ohmmeter. Because you have an oil pressure gauge they found it wasn't necessary for the idiot light anymore.

Thanks again gtogreen, I've done the tapping, bathing and blowing as you've suggested. I can do without an idiot light (despite what my family might say), if the idiot light is the oil pressure warning found on other cars. I'm less clear with the filter bypass light. If I understand it correctly, theoretically I could still have good oil pressure but the oil could be bypassing the filter (returning unfiltered oil to the engine). Has anyone blanked off the bypass for peace of mind, or am I just over-thinking it?

If the bypass and switch are prt of the head then you could replace the whole thing with a spin on filter head.

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Cheers Dave.

Thanks Steam, I could certainly do that (and save a whole lot of swearing at each oil change), however I'd prefer where possible to keep things original.

I should also say that although these are my first posts, I've been lurking on this forum for a few years now and have really valued the wealth of knowledge embedded in the threads, and enjoyed the exchanges between members. It's a fabulous resource!

I rapidly grew tired of the original oil leaks from the original filter housing. Originality only goes so far before it becomes tedious. But kudos for sticking to the original designs.

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Cheers Dave.

They were not a reliable design. I have a bunch of those all with stuffed bypass switch. If you don't want a spin on I would fit the earlier design without the switch.
I have some if you need one. Real Cheap.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Anything cast into the aluminum top housing between the 2 bolt holes ?

Look like it take a 8G706 or Cooper S felt filter.

Appreciate your offer, drmini. Is there any harm leaving the one with the stuffed bypass witch in place (just removing the wire)? I change oil and filter regularly and drive minimal miles.

Karcraft, there's nothing cast in the alloy between the bolt holes - just the sender for the warning light.

If the switch isn't leaking it's fine to use. All my dead switch ones came off working motors.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Great. Thanks drmini and all for the advice. Appreciated.

TBH judging the oil change frequency by miles driven and the state of the oil is by far a better way than whether filter is blocked or not so you are actually better off without the switch and dummy light.

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Cheers Dave.