Although the control voltage comes from the radio, the actual power for the motor comes from fuse 6 in the trunk fuse panel, so check that for looseness or corrosion. I've never seen a radio fail this way, although anything is possible. But power antenna mechanisms are notorious for failure. Although a do it yourself'er could probably replace a broken limit switch, in the real world, replacing the entire power antenna may be the route of least frustration ( where do you find a new switch ?). The nylon cord is sold as a replacement item. Do an internet search for hirschmann antenna. But I'd make absolutely sure the power and control voltage were OK first.

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Resistance is Futile.