I am trying to install a navi to dvd interface in the trunk area, but I can't find a power source that I can tap into. I know there is power to the navi unit but I don't have the schematics nor the tool to test which wire is it. Help please.....

 

IMO if you want to be safe and do it in a way which you can remove it incase of warranty work in the future, run the ground to anywhere in the trunk and then run the 12v+ through the backseat (under it of course) under the side panels up to the fuse box and connect it to a fuse using an "add-a-circuit" unit (usually about $10 at a local auto parts store). This way you can have it safely integrated into your electrical system and easily removed without splicing in any other wires.

If there is a warranty problem with your car and the navi, you can easily remove the modification without leaving any cut/open/spliced wires (which the dealer would not approve of)