I don't seem to be getting smarter here. 1988 XJ6. May have bad coolant sensor. I detached the coolant reservoir, took off the large knurled ring and now can't see how to remove the sensor from the tank. Does it have o-rings and you just pull it straight out? Everything is plastic so I did not want to ream on it until I find out how it is supposed to come out of the hole.
This is the one which enters the tank on its rearward end.

 

Ooops, I should have said coolant level sensor.

 

The level sensor just pulls out.
The hinged plastic part needs to be installed so that the end drops down once the part is reinstalled. Note the orientation when the part is removed.

bob gauff

 

The sensor did not readily pull out. I will wait until the replacement arrives before getting more aggressive with it.
I did jump the contacts on the wiring to the dash, as suggested by postings here, and, sure enough, the low coolant message disappears, suggesting that the sensor itself is kaput.

 

Sure enough, with a little persuasion the sensor pulls straight out. Installed new one and yahoo, "coolant level low" warning is now gone. One tiny victory.