A3 xenon not working help!!

[Gurbz]

Hi there, my passenger side xenon is not working and wanted to know how do I find out what could be the problem ??? I brought the car accident damaged on the passenger side and brought a new headlight... I used the old ballast and bulb. How can I find out if it's the headlight ballast or bulb or the wiring...driver side works fine... Thank you in advance

 

[SootySport]

Swap the working parts over from the good light to the nonworking one to prove.

 

[NHN]

As above, swap bits across to prove there error