Heat Exchanger Gauge

Recently discovered a pair of these gauges on the 820 hp. Man's. Appears they each have a small micro-switch inside their lenses but for what ??

YES, but the other thread was closed and I did not see any microswitch in the the posted photo of the gauge on the other thread. My dash is currently a massive clump of wires till the new dipped carbon fiber panels arrive so not able to do any testing yet but a low HE alarm would be great as unless two salon floor sections are removed, can't even check the water so do need to test these alarms. I know some of the old warning lights were blown-out bulbs; all of which will be replaced with LED's when installing the new panels. Only have about an inch from caps to ceiling but I guess that's the "price" for the extra hp. vs. what I believe was the, back then, standard Detroit's.
A review of the purchase survey noticed it recommended adding over flow tanks but for some reason it appears Man doesn't use them.

I recall only water temp gauges but there were a bunch of various alarm lights. I dare not put my hands on the birds nest of wires & switches the tech doing the project up there left while we're awaiting new panels, gauges, switches, LED's, even though he of course labeled and wire tied them.

I'm sure there are a good number of those who hardly ever check up on many things in the ER. Personally I've never found more then a slight non full situation in previous boats but I think these gauges are great; and even that much better assuming at this point their hooked to an alarm. Old neighbor over-heated one of his Cummins and the resulting repair estimates were in the 30,000. range. The guys wife went bat **** on him and he sold the boat.