paultrantz

HI Folks, i have just bought an IS300 Sportcross, 54plate with only 53000 miles. love the car but i got it knowing the sat-nav didnt work. the screen works but the main stereo head unit has been replaced with a sony aftermarket unit. can anyone help?? i have the original head unit and i am assured that it works. the only thing i know is missing is the nav ariel that goes behind the glovebox.... the nav unit is in the boot as it should be.... is this a common fault??? help would be greatly appreciated. thanks Paul