happened out of the clear blue? any related (electrical) changes preceding this issue? I'd start by pulling the bakelite connector off of the HL switch and pulling the switch out so you can access it's terminals & (1) ohming the switch terminals in the on/off positions you mentioned to see if it is an internal switch issue & (2) jumping fire to the various connector terminals in the bakelite connector & see if the appropriate bulbs light up. this'll point you in the correct general direction to start on if it is the switch or the wireing & www.mymopar.com has the colors for you