is under the passenger side fender undercover. If you remove the passenger side front wheel and then the under fender cover closest to the door you will find a large wire harness that goes into the car. You can punture a hole in the rubber cover and run your wire through that. If you run the wire down to the A/C drain vent like Adam said be VERY careful that the wire is secured AWAY from the precat/header. I have seen several people that have done that and the wire melted against the precat/header.
Kyle "Grumpy Bear" Puckett 93 300ZX TT(Auto) SGP Stage XIII + some :-) ICQ #727815