Help! New power antenna continuing to run

[my81c3]

Replaced the dead power antenna on the '81 with one from Eckler's quite awhile back. After the usual fit problems were overcome, it worked fine for the few times I tried it. Speakers needed replacement, as well as a possible radio problem, so occasional use of the car has been without switching radio on or off at all. All of a sudden out of the blue the other night I hear a motor noise in the garage, narrowed down when I passed by the rear of the car. Antenna is down, but somehow thinks it's not, and attempts to keep running. Tried turning ignition and radio on to bring it up, but nothing stops it other than unplugging, either at antenna or at relay behind console. Sound like a problem in the antenna internals or the relay? Anyone have a clue?