1984 Nissan 300ZX headlight problem

Can anyone out there give me a clue. My Z has an unusual problem. If I turn on the headlights they come up and go on. The problem is when I turn them off. The lamps go out but the headlight motor starts going and does not shut off, even if the ignition is off. So in other words the headlights continually go up and down until the battery runs out or I get lucky enough playing around with the switch or the up button on the side of the panel. At this point I just don't drive it at night, but end up racing home like a vampire getting out of the sun if I happen to be out when the sun sets. Any suggestions. Thanks!