Thank John..see below
I'm having a little trouble following your description. You say "on the Exhaust Injection pipe, just before it meets the heat exchanger". By "heat exchanger", do you mean "mixing elbow"?
Well, I may have my terminology incorrect. I'm calling the main thing in the center of the diagram, with "VETUS" on the side the Heat Exchanger, when specifically that would be part #36. Part #34 Vetus is calling a "Exhaust Injection Pipe". Truthfully I've not taken the time to trace it around to see if it's indeed straight exhaust (no water yet).
Also, what is item #9 on the schematic? And what is #49 (including ##34&48)?
From the Scematic:
#49: Injection Pipe + Plugs
#34: Exhaust Injection Pipe
#48: Plug G 3/8
It sort of looks to me like the "thermo switch" is inserted into the exhaust opposite the point in the elbow where the raw water from the heat exchanger gets dumped in, in which case that might be a good spot to have the temp sensor. But usually when you have a heat exchanger, you're concerned about the internal coolant temp, not the raw water temp.
Good point about the internal coolant temp. I've got a single temperature idiot light on my engine guage panel. Don't know if it does anything though.
I think you are correct, now it makes more sense to me. The term "Exhaust Injection Pipe" threw me..Exhaust isn't being injected, it's getting injected with raw water.
I'm attracted to that sensor #8 below since I can easily get to it, and can easily rig some sort of temperature alarm, or even a temp guage if I was lucky. That is, if I can figure out what it does. "Thermo Switch" sounds like an all-or-nothing" sort of a thing.
Typically, how do these sensors work. If I remove the sensor, and heat it, what am I looking for (ie what does the wire transmit).