For water temp, buy a 98 F-body water temp sensor and wire it in with a new connector. The additional third wire is the temp sensor lead for the gauges. As for oil pressure, you have a few options. I removed the stock oil sending unit and put the original factory pressure gauge in it's place using an adapter made from a broken sending unit I drilled out and tapped. You can also tap out the fitting that bolts to the side of the oil pan above the oil filter. Use the factory wiring for the oil pressure gauge. The voltage sensor is independant of the engine wiring harness. The tachometer can be made to work using an adapter made by BakerElectronix.com.