Oh, you have aftermarket gauges!
Look up the specs on the sensors that were provided and compare to the Bosch PST-F1, which is a sensor that measures both pressure and temperature in one compact unit. You'll need a 5V reference to drive it, either from one of the factory ECU's or any of the aftermarket ECU's. If you're still on some version of mechanical injection you can buy a 12 volt to 5 volt converter for under $10.
http://www.bosch-motorsport.de/content/downloads/raceparts/en-gb/54249355.html#/Tabs=9007199309001995/