My Dodges have a deal that if you shut the engine off before the lights, the lights stay on on a timer 1-2 minutes (I dont remember). Your computer might not see the ign. off signal and activate this feature. If you turn the switch back on momentarily it will cancel the feature, kinda like you described. It could be a bad ign. switch, and or light switch. Do the lights stay on constantly or do they go off after a few minutes? The other thing is are the parking lights on also? When the feature is activated the head lights are on without parking lights. Hope this helps point you in a direction....Good luck !