Sorry I have no idea where I got it! Just found it in my packrat piles. It's brass and meant to screw into a water manifold of some type, but just search amazon for snap switches - there are a bunch. It's amp rating was under what the fuel heater draws, so I put it inline with the fuel heater relay coil, which only pulls a few milliamps when it activates.

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2005 CRD, owned since new.
GDE Hot tune, 2.5" lift w/JBAs, 235/85 Duratracs, Weeks2 kit, Provent, Facet lift pump, Cat fuel filter