Earth issue? dull oil light random when driving

[Shinnster]

Hi all,

i'm having an issue that i think is the earth from the oil pressure switch but just looking for confirmation really that nothing major is wrong!

I had an issue with the buzzer and oil light going off (even though my pressure gauge reads ok when it happens)
i had diagnosed it as  a faulty switch / sender , the one below the water pump on 1.9 DG.  I am unable to get any of my sockets in that gap to get the thing out, so as a temp fix i removed the wire and put it onto the left side of the engine with another earth .

Now though, when i'm driving, at completely random times, it could be after 5 minutes, or 2 hours into a journey the oil light comes on really dull for about 6 - 8 seconds, then switches to the battery light for a split second then goes away.

so is this just me and ive done a dodgy attempt at earthing it? (which i'm guessing is the answer as it was fine before i done it) it was all cleaned up before i done so .
Any tips on getting the sender thing out ? as i'd rather just have it back to how its meant to be

[maxstu]

Check the dash multipin is fully seated.
Check the oil switch wiring back to the yellow connector for damage.
Release the three bolts on the waterpump pulley. Slacken alternator belt and remove waterpump pulley.
This will give better access to switch.
Remove switch and test.