It's about 12 gauge. I was trying to go with just the factory made wire with inline fuzes but it is too short leaving me with just 2 options. Install under the drivers side dash using existing holes there or make a hole on the passenger side or dismantle passenger side covers and weave through there using the door hinge panel wiring boot hole. What ever is going to happen it looks like I'm going to go with a heavy gauge pair of wires from the battery to a hook up block inside the truck. The main things I can't do is reduce the amperage rating of wires, loose amps available due to wiring and heat due to heavy amp draws, have the radio in an easy to steal location, mount the radio where a good short ground isn't, not have the radio power supply + and - direct to a battery. I guess I'm going with heavy gauge wiring. Then we'll be seeing if the battery and alternator can keep up. I'm also looking at changing the battery terminal connectors to a better type that supports a solid connection of my radio. A little washer crimp on style connector isn't going to cut it for me.
Oh yah. If you are looking for a spot to go through I'm not sure if it's the same for all models but if you take a solid rod with thin wire taped to the end then stick a hand under the dash where the wires go through the firewall by the fenders you can poke the wire through to the engine compartment with the rod. I started with a fishing leader line then used it to pull through a weed eater plastic line to pull stuff through. Went pretty smooth till I laid the line out and didn't like where it was going to end up having the radio.