I was suprised to find how little information there was on the Audi B5 Nav Plus Retrofit, it seems like this would be a common mod, I guess not. So I decided to find someone with a little experience, Jeff in the parts department has actually retrofitted the RNS-E Nav Plus system into his B5 A4 and he did a killer job, the fitment is exceptional. The install took Jeff several month to complete.
The first roadblock was the can-bus communication between the navigation and the radio was tough to establish, the time on the cluster did not match the Nav Plus screen. Second the Bluetooth was difficult to wire (make sure your wiring connections are 100%) it is most likely not a faulty Bluetooth module. The B5 A4 was never designed to have this system, so needless to say you will need to modify the heater by removing approx: 3 inches. Jeff did this install on 3/20/2008 so a tone of information is available, regardless this is not simple but well worth the effort.