Radiator Expansion Tank
The Red arrow is the connecting pipe to the Radiator on the 'Off' side.
The Blue arrow is the connecting pipe to the engine block on the 'Near' side.
The Yellow arrow is indicating the 'Low Level' connector cables which pass to the Dash panel indicator.
THe Green arrow indicates the pipe from the base of the tank to the heater system at the rear of the engine..
If the expansion tank overflows or the expansion connecting pipes leak. I have found this connector plug and socket will short circuit and indicate a LOW level on the dash. The cure is to clean these connectors, by taking apart, reconnect, then fill the socket and plug with grease to ensure no liquid is allowed to leak down.
Radiator Expansion Tank Pipes