Drill a hole in the firewall just below the engine compartment fuse-box. Use a grommet in the hole, feed the wire through and seal around the wire using silicone.
This is the right way to do things.
133whp-126ftlbsTQ Eclipse CD8443,JBL Px300.4, JBL GTO7001, PPI 356cs, JBL p1024(Hooray!) SubThump enclosure, RAAmat BXT, Damplifier Pro
Hatch Nation #140
Caeci caecos ducentes