I have a 2003 Honda Civic EX 5spd with aftermarket headlight assemblies which have separate low beam and high beam lenses, and am currently experiencing what I believe to be a possible ground issue. The driver's side low and high beam, and passenger high beam are all on but very dim when the headlight switch is set to low beam, when high beam is selected the passenger side functions properly but driver's side does not change. I ran a test lead from the driver's side low beam (grounds to lens assembly) to a new ground which causes the high beam on that side to brighten and low beam to dim. After that I unplugged the driver's side high beam bulb which caused both the the high and low beam on that side to become inoperative but did allow the passenger side headlights to start functioning properly (test lead was removed at this time from driver low beam). I'm thinking there's probably a ground, in the assembly or else where, that's not allowing proper current flow causing the power to search through the circuitry for another route to ground and in the process is powering the high beam bulbs. The only recent change to anything related to the headlights was a recall relating to the headlight switch wiring or contacts. I did also trade my HIDs for Hella 100 watt bulbs, but don't believe this would have any relevance other than the HID bulbs did not ground to the lens with how they were wired being the reason I only just found this problem.

 

Could be more than one problem. Have you tested the light switch itself?