Headlight Switch

Why may my parking lights and tail,  stay on after sentiniel goes out and the headlights are manually off.?

1985 2 door coupe deville. 
(Update, i took the switch out, as soon as fuse is inserted in the tail lights
and side marker lights stay on.) so with switch out of the equation, its relay or bulb or wiring?

  Any suggestions?

Check for bcm codes and operation of headlight switch with voltmeter, I not sure if it has twilight sentenal module, if it does  - another possible cause.Hope it helps