Miscellaneous Switch

ok here's one for all you geeks out there.

My speedo packed up today whilst going out to pick up a steering wheel. Luckily I had a spare from an P6 auto to hand so I got home and started to replace it. for some reason fittting the speedo cable was an absolute ****** today, but whilst my head was inside the drivers glove compartment I found a small round switch. no wires were connected to it so nothing happened when i operated it. i dont have any photos but it is located right above the bonnet replease and it is a pull/push type.

who knows what its for??

I've just removed an identical sounding switch from a Rover P4. This one had a black wire to earth and another linking into the low tension lead between the coil and distributor. So when "on", the LT circuit would be earthed preventing a spark.
I only had a quick look whilst wrestling with the speedo cable, which was being a real b****.
I will check again in the morning as i am on back shift, will try to get a photo of it.
That sort of thing was a very common 'anti-theft' idea back in the 60s/70s. Lots of people fitted similar things. Or a switch for an early home-made electric fan addition but an unlikely location.