Perhaps you've simply been trying with the microphone input, rather than the stalk input? The connectors appear rather similar.

EDIT: I just now hunted down the dock here with a PCATS tuner inside, and tried the same tip-to-collar test there. FAILED. Then I tried what I thought was the MIC input, and.. behold.. it lives!

That thin grey coax of the stalk input *really* suggests a MIC input to me!

Cheers