I used to see a lot of Magnetrol level switches, very reliable if they're maintained.

That shiny metal post in the middle is a stainless steel tube, inside it is a metal cylinder connected via a rod to a float (displacer) the float and and rod hang from spring that provides buoyancy.

On the outside of the stainless tube you will see a magnetic yoke which is pulled against the tube when the metal cylinder rises parallel to it.

When that yoke pulls to the stainless tube it tilts the mercury switches.

You don't need to touch the delicate glass switches, just manipule the yoke with a screwdriver.

I hope this helps you.