[W126 Coupe] Passenger headlight bulb only glowing at half strength and it is not the bulb

[calvin young]

Hi guys,

I could use some help with a light problem.  It seems my left headlight is 
glowing dim.  the light is half of what it should be.  This problem seems to 
come out of nowhere although the mechanic is changing out the driver's door 
and working on the wires.  He may have shorted out something, perhaps this 
caused a relay to malfunction.

Changing driver's bulb for passenger bulb changes nothing.  Anyone had or 
heard of this problem before?

Cal