Tip: Dual-circuit pressure switch for Hobbs

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/honeywell-sensing-switch-5000-series-productsheet.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.

The one Van's sells does just what you say.
Oil pressure switch for activating Hour Meter and light IE SPDT PRES-15 SW $35.00
Pressure good = one terminal goes to ground (switch body)
Pressure bad/low = other terminal goes to ground

as long as you use low-side switching, it works.
i.e. +12V ---hobbs---switch---ground
+12V---warning light ---- switch---ground

The Vans part includes a sheet showing how to hook it up.