Hopefully this helps someone avoid buying the wrong part:
I'm planning on installing a Hobbs meter. The standard way to activate the Hobbs appears to be with an oil pressure-based switch. When oil pressure is present, the switch closes, and the Hobbs meter runs. I'm also planning on running a panel light that is on when the switch is open, indicating low/no oil pressure. For this application, you need a 2 circuit
oil pressure switch.
The switch sold by Spruce is Honeywell part number 76575, which is only a single circuit (normally open, suitable for activating the Hobbs meter). The one you'd need to also support a panel light is Honeywell part number 76579, which has dual circuitry: both NO and NC terminals.
Information about these pressure switches can be found in their datasheet: https://sensing.honeywell.com/honeyw...oductsheet.pdf
I obtained mine from eBay, but there are a number of online vendors that sell this part.
Now I've got an extra brand new single-circuit oil pressure switch that I'll either return to Spruce or sell over in the VAF classifieds.