You could just run the one wire through the firewall to the battery.



I would put the circuit breaker between the firewall and the battery connection.



The fuse inside the firewall is not enough. Even if the fuse inside the car blows, a bare wire going through a firewall can still burn the car to the ground.

The other wire goes to a ground - I used the stud that holds the top of the floor panel covering the stereo.

This would keep your GPS power available all the time, even when you shut off the car. Based on my experience, this is better than having to leave the car running if you need the GPS. OF course you can shut off the GPS when you want to. I have left my GPS on with the car off for long periods with no problem starting the car.