I got hold of another factory tuner and harness.
Now I'm getting a voltage from the power antenna wire.

It seems that the 12v is there from the word go.

Switching on the ignition: 11.62v --> 12.42v
Switching on the player: 12.35v
Switching on the tuner: 12.31v
Switching off Rio: 12.42v

Is this the right behaviour? I imagine -- could be wrong -- that the antenna stays down when using the player, and only comes up when the tuner module is selected.

Perhaps there's some problem with the power source for the whole set up being via the ignition and not passing through the auxiliaries circuit.

I would have thought though, that the tuner would not be giving out 12v when it wasn't in use.

Any clues?