The nav controller would normally live in the boot, but needs the cabling as well. Non-nav cars didn't have the nav harness, so if you have the cabling there but no nav unit then it's been taken out. Certainly if you have the widescreen nav screen then at least some other stuff has been fitted as it requires a gateway ECU to allow the AVC-LAN and BEAN networks to talk to each other, without this the heater controls don't work. I retrofitted the full widescreen nav system to mine, details at http://www.ult-search.co.uk/gsnav/, you may be in luck with a LandCruiser 100 or Prius nav unit.