if your car does not have the Nav factory installed, a retrofit of a Nav system will call for several components, the wide screen, the nav computer (MK1,2,3 or preferrably 4), BM53 (or BM54 for euro) radio module and a full harness that will take care of the retrofit.. i have a factory retrofit PDF, if you care to have i can send it to you... you will need to tap the special retrofit harness into the speed sensors, the gyro and the whole nine yards - the retrofit is more involved than $200 in labor charges.. so, have him do it, assuming that he does it properly...