Web Forum for Singer Cars

I intend to change the oil of my Singer Lemans for the fitst time. To my surprise the sensor end of the oil temperature gauge is fitted to the sump plug (didn’t find another at least). If I undo the plug, the lead (it seems to work without electricity, no clue how) will be twisted several times. The lead is long, so probably not much harm done. Ideas for improvement would be welcome. Secondly, how can one undo the ‘lead’ from the gauge itself? There seems to be no thread. Is it shrunk onto the gauge? I’ll paste a few photographs in the hope it clarifies my challenge to some extend.
Thanks for all feeedback.

With the length of the wire it likely is not thermal like a normal house thermometer. Ok, this is so new to me I won't even hazard a guess.