Now I'm confused.

I've just called Blaupunkt's service center. They say that if that if the telephone power input gets shorted to ground, the stereo will go to tel/nav. They recommend not using the factory harness to avoid this issue. However, I've noticed other Balupunkt users on this forum just plug in the factory harness with no conversion necessary and not have an issue, including one St. Louis owner.

They also said the antenna will have nothing to do with it.