what is the sensor/switch next to the hydro filters on a L553?

[scottlandyard]

what is the sensor/switch next to the hydro filters on a L553? Im now wiring up my burner and was wondering what this switch is? its 1/8 thread and has 2 male plugs on it. Looks like a pressure switch that would activate a warning light? Thanks in advance. Scott

 

[skidsteer.ca]

That should be the indicator for the hydrastatic charge pressure. There is likely no continuity between the two terminals of the switch, then as charge pressure builds to a safe level (60 to 100psi ??) it closes the switch.
Ken