If you keep everything from the slavaged vehicle in the harness you're okay, including the gas pedal assembly. The gauges will be the big problem, since most of the newer ones read off the OBDII computer. There are newer replacement/custom gauges that will do the same. You don't need a complete wiring harness for the donor vehicle as long as you UNPLG connectors, DON'T CUT WIRES. Then you just need the wiring pin-out charts for the connector to the firewall, the computer, and the instrument cluster. Those three will provide 90-95% of what you need. A few others you'll have to trace out.