Originally Posted by trapdoor

If it's a Philips tuner then it will be a very early 4:3 model. Lowe is possibly 4:3 or 16:9 and Lear tuners are the latest which will do both and some are Hybrid digital and analogue.

The 4:3 tuners will usually kind of work, but being an early tuner may not be at all compatible with Mk4 Navis. Have you tried unplugging the blue connector on the Nav and seeing if you get the basic 'tuner only' menu? If not, then it could be a faulty tuner?