if the cab is wired for a cb (its an option so not every cab will have one ) then pop out the rotary light switch and have a look in behind - you may find a coiled up coax cable with a 12 volt supply coiled up along with it . It can be quite far in so have a good look . My cb is in the din slot to the left of the rotary switch or below the central locker ( the funy shaped sloping door one ) the coax cable and power will just be long enough .Thats an XL Globetrotter cab