I used a 12ga wire from the battery and I have a large suv so the run was pretty long and I have had no problems. I only have the PC, a mini keyboard, mouse, and usb wifi so I'm not power a ton of stuff either. Anyway you want to run a 8, 10, or 12ga depending on how much you want to power from the battery to your PC, then run a wire inside from something that only turns on when the key is on. and then tie the third wire to a GOOD ground point. This could be the battery but I'm sure you can find a easier point inside the vehicle.