where is the ballast?
 

Where is the ballast in a 2007 c70? Does anyone have a diagram or instructions for changing it please? I think it is in the fender but I don't know how to get to it and I cannot find any videos or diagrams on the internet.

Low beam only works sometimes, have changed the bulbs, and ignitors. Still having the same problem, so going to replace the ballast and if that does not work the wiring harness. Failing that I will be replacing the entire headlight.

Following
 

Same issue on my 2008

depending on model/year, low beams also have a relay inside the CEM which can fail or go intermittant. To diagnose you'd need to catch the problem in action then see if you are getting voltage to the lamps. There's some vids on Youtube how to bench test HIDs to determine if the ballast is good or not.