how to get wires into passenger compartment from th engine bay. I found an offwhite plug in the firewall is this a hole I can use

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This is on a my2002 impreza. It may be the same for your case.
http://mechatro2.me.berkeley.edu/~satrya/pics/photos/imputaillight/rev063.jpg

On the passenger side of the engine bay there may be what looks like a vacuum hose going into the passenger compartment. Some wires can be passed through the surrounding grommet if their not to thick. I haven't seen an 05 though.

I found an offwhite plug in the firewall is this a hole I can use
I'm not familiar with the my2005, but if you're curious, you can try and open the plug, and run something stiff without sharp edges through. See if it comes out somewhere on the other side.

Another location that Mulder often points out is a grommet near the brake pedal. From the cabin, look for a blind grommet near the pedal, remove them, and try to run something through. It should come out into the engine compartment. You may have to raise the car to see where it comes out, as it is rather low. My guess is this grommet should still be available for the my2005 imprezas.

remove the washer bottle and under the power booster push out the rubber plug, this will put you right behind the pedals