These instructions are for a '92-'96 Camry. I'm not sure if it's the same for '99, but if you have the time and patience and wan't to avoid drilling a hole in the firewall, this is the way to go.
This was posted on CMPL by Gibson99; http://www.camryman.org/cgi-bin/config.pl?read=168738
Pull the driver front wheel, and the fender liner. you'll see the rubber grommet that has factory wires going into the cabin, and a plastic ring going into the engine compartment.
Other than the above route, your only other choice is to drill through the firewall (from what I know). What ever method you use, do yourself a favour and use 4ga pwr wire if possible (ask Camry2000 :wink: ) and don't forget to use a gromet to prevent the wire from being severed and starting a fire in the car.
Besides that, welcome to TN![/i]