If that is a 9C1 vehicle (VIN starts with 2G1WF55K) then you don't need to penetrate the firewall for power for a single radio.. it's all in the accessory wiring harness.
Look underneath the floormat on the passenger side or under the dash beneath the kick panel and you will find a blunt-cut wire bundle with a lot of wires and plugs sticking out of it. You will only need the wires sticking out of the end. Look for a 12-gauge black, 12-gauge orange, 14-gauge dark blue and dark green, and 18-gauge pink, yellow, light blue, and light green.
Orange - 12V+ constant
Black - Chassis ground
Dark blue, dark green - Relay-switched 12V+
Light blue, light green - Relay trigger lines for relay-switched 12V+ lines. Paired light blue/light green and dark blue/dark green.
Yellow - 12V+ on with ignition and off in start. DO NOT USE TO POWER A RADIO DIRECTLY - attach it to the relay trigger lines and used the relay-switched outputs if you want ignition-switched power.
Pink - Same as yellow, but does not cut out in start.
If you don't want to turn the radio on and off with the ignition switch, just use the orange and black wires for + and -. If you want to turn it on and off with the ignition switch, tie the light blue and yellow wires together and use the light green wire and black wire. for + and -.
Oh, also, instead of using electrical tape and twisting, go pick up a pack of ring terminals and butt splices from AutoZone, and a set of crimper pliers from Home Depot. You can also get split-loom tubing from AutoZone to insulate your under-carpet wiring with. And while you're at the Depot getting your crimpers, pick up a bag of
black zip ties to secure everything with. All of these items combined and used properly will give you a secure, reliable, and professional install that will outlast the car.