The cable does not go through the firewall. It connects to a switch under the glove box just to the right of the center console. When I removed mine I took the whole center console and radio out but I do not think you have to...although it was a little easier when putting the wire for the temp back to do so.

Let me just warn you taking out the HVAC controls is a 8itch and a 1/2. It took two of us to get the plugs out of the back...our hand were too big to get back there...one pressed the tabs while the other pulled the console!