you can also check through the fender. if you take off the plastic cover that is there between your front wheel and the fender, there is a passage there too. well my friend's 92 acura legend was like that so you's might be as well. but first check for the rubber gromat like james said. if you don't see any then my idea can be your next option.
There will be a rubber gromit but odds are it is going to be on the drivers side of the firewall.. I'd check there first. If all else fails drill a hole in the firewall on the passanger side.. make sure you do not drill into anything else but the firewall! ..
only problem with running it through the fender is if the wire gets lose and falls into the door jam.. would not be a good thing have your system short out because the wire got damaged from the door opening and closing.. if you go that route make sure the wire is secure