I have 0 guage power wire in my 1999 Oldsmobile LSS and im not sure as where to run it through the firewall. Has anyone done this on this car or a similar car like an eighty eight.

 

0 guage will most likely need a hole that you have to drill yourself.

 

The W bodies have a big factory grommet under the passenger firewall carpet, those might too.

 

yup, in most GM's, there is a big grommet for the factory Chassis wiring. It has way too much rubber/plastic around the wires.
I drilled a 1/2" hole in the same grommet, right beside the existing wires. Obviously you have to be very careful. I started with a small pilot hole and worked my way up with 3 different sizes.