Eric,
The pressure sensor is a Nason
SM-2B-115R/443. It's just a pressure actuated switch, so it's nothing more complicated than a NC dry contact.
I'm not sure if I understand the mistake Fe_Will made in wiring the sensor. Standard wiring is signal to one side and common to the other, as with a limit switch. Reversing the connector where it plugs into the DSC wouldn't cause any problems. I think he's saying they wired it by chopping the end off a standard PWM cable, and they accidentally wired red and black to the switch instead of white and black. I assume a short from 5V to common would damage the DSC in some fashion, yes?