Question for all you A/V experts!

I am about to install an xbox in my TL. I currently have one of those cig lighter dc to ac converters and was wondering if I could just hack off that cig lighter male plug on it and splice it to another wire that is connected to a 12V source? If so where can I find that source? Can I use an empty slot in my fuse box using an add a circuit? Your help is appreciated!

 

i would not use an empty slot... I would either tap into the cig adapter wires, or I would create a relay and battery-wire install like an amp, but with a relay turning off the inverter with the key off...