Volvo Repair: volvo 240, marker light, high beams

Question
  I have a 1990 240 DL .  for some reason when I turn in the headlights they dont work. Also the rear lights and the dash lights dont work when the headlights are turned on.  All seem to work with just the parking lights on.  The high beams also work. all marker lights working fine.  Any ideas ?  I have changed bulbs and checked and changed some fuses. Im lost!!!  I have just recently replaced a left side marker light and feel it must have somthing to do with this repair but I dont see how.

Answer
unless the marker light has blown a fuse it should not have affected the other lights.it could be a bad headlight relay which is a silver relay under the hood near the left inner fender,or a bad head light switch.with the interior lights not working sounds like a abad switch.be sure to check the rheostat is turned up for the lights this is the knob under the headlight switch.if this fixes the interior lightas I would suspect a bad headlight relay.