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