2006 Lariat 6.0 Stereo Question
I recently added a Sirius Radio to my truck and while the factory 6 disc head unit was pulled out I saw that one of the 2 plug sockets on the rear of the radio was empty. If facing the rear of the factory unit, it's the empty socket on the left side. There is a numeral "7" stamped in the metal above the plug socket. What is this empty socket used for? I've searched every Ford online resource I can find with zero luck.