unusual oil pressure sensor Farmall M

55 50 Ron · Sep 20, 2022

Here is a sensor on a Farmall M that I do maintenance on. It is tee'd into the pipe to the oil pressure gauge. I just discovered it recently and haven't had time to fully investigate, but it appears to have just one wire attached. That wire ties to the hot side of the starter switch. Probably a farmer's safety switch if oil pressure is lost, but seems it's been disabled since the other wire is missing.

randy hall · Sep 20, 2022

powers the hour meter.

Janicholson · Sep 20, 2022

It could be to excite an alternator if closed with pressure, and connected to the #1 terminal of a Delco, or the L terminal of a Hitachi. That would avoid diodes and push buttons in the circuit.

steve_in_mo · Sep 20, 2022

Might have been used as a low oil pressure shut down on an engine for an irrigation pump.

kshansen · Sep 21, 2022

That appears to be an older Hobbs Pressure Switch and they can be had in many pressure settings and normally open or normally closed or a combination of the two. Believe there were some that worked on vacuum as well. When new there would have been a sticker on stating the pressure settings and part number. One of the common uses was to activate an hour meter.

I used a switch like that to "turn on" the 12 volt alternator on my BN when I converted it to 12 volts years ago. It was suggested by a guy at the electrical shop we sent all the electrical work for the heavy equipment I worked on. As it has been there doing it's job for well over 20 years I think the guy knew what he was talking about.

unusual oil pressure sensor Farmall M

55 50 Ron

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randy hall

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Janicholson

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steve_in_mo

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kshansen

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