Lighting problem, help plese.

[popnGEAR]

Since October my driver side headllight bulb hasn't been lighting up very very dim and I just assumed the bulb was half dead or something. One of my friends saw it and told me that it probably wasn' the bulb and that it was most likely a melted harness. I got that checked at a dealership and they saw no visible electrical problems and said they required further diagnosis (I coudln't do it because i had to leave and get back to work). When I got home today I swapped driver side bulb with passenger and vice versa and here's what happens..

If both of the bulbs are in their original position then:
driver = dim
passenger = ok

If I swap then:
driver = dim
passenger = dim

If only one bulb is in on either side then it won't light up period.

Now I've put the bulbs back to their original position and driver side doesn't light up at all now.

I'm using PIAA H4 Superwhites.

Thanks in advance.