Might sound silly, but are you absolutely sure?
I mean VW's have the permanent and switched live exchanged in the ISO plug, that's an old porblem with them (so much for ISO). But each one I saw had them.
Maybe a previous owner had not known that situation and, to get rid of the unwanted switched one, has cut it off and sealed the blank end?
AFAIK the radios anyway take the power from the permanent live. The switched live is just that: A sign that you want the radio to operate :-)
regards
Wolfgang