Dang that was fast, I received the monitor in the mail today. Northern Indiana parts surplus...
Looks fairly simply. I have not examined the circuit board yet, but it consists of a single LM339, which is a general purpose single supply quad voltage comparator OpAmp, a 2N3904 general purpose NPN transistor, and a handful of resistors and diodes.
Without tracing out the circuit, I am confident my initial hypothesis on how the circuit operates is correct...
And here is the harness which should have three resistors in it. Over the next couple of days, I'll figure out a schematic and values.
It is not a sophisticated circuit by any means.
I'm gonna download a datasheet on the LM339. With any luck, their circuit will be right out of the book.
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