There should be a large rubber grommet on the firewall under the dash left of the brake pedal. Instead of drilling a hole I usually put a small slit in the grommet and push the power wire through next to the factory wires. Be careful not to damage any factory wires. Quick clean and easy!
I know this is an old post, but did you ever find a solution? I just recently acquired a 96 wagon and I think it's got the sedan struts. Looking to stiffen it up a bit.