Ok, so this sounds like the same issue that my stealership diagnosed about a year ago, and their answer to the problem was to quote me $2,000.00 to replace the entire headlamp pod assembly!!
They can spend my money faster than I can make it!!
The service tech said something about seeing/smelling some burnt wiring. I said I'd think about it and got out of there as fast as I could.
My issue occurred right after I upgraded my xenon bulbs and the left drivers side bulb would only flicker occasionally thereafter, wouldn't fully light up. I don't really drive my car after dark much and when I do, the loss of the left light wasn't really enough of an aggravation to prod me into resolving the problem, yet.
But maybe now is the time to work thru this with another fellow 'bimmer and get it behind me (us).
And so, here I am and how I came to find this thread thru the search function for "xenon ballast testing".
So, from my "sparks and magic" electrical courses in mechanical engineering school, I believe a ballast is nothing more than a transformer, boosting the vehicles 12V dc operating voltage up to a much higher level for the xenon lamps to function.
Damion0097, you're already a few steps ahead of me in having diagnosed & replaced the headlight control module & ballast. Have you by chance measured with a volt-meter to see what the output voltage from the ballast is? Probably by measuring the output voltage from your good working driver's side ballast would tell if it is putting out the correct (same) voltage or not.
The next step I would think would be to perform a continuity check on all the wires in the wiring harness between the ballast > control module > xenon bulb. Using a multi-meter, set to the Ohms (Omega symbol, horseshoe) setting and the meter display should show something like "OL".
Touch one of the probes to each end of the same wire. If the wire is good (as in not melted in to), you should get either a tone (if you meter is so equipped) or the meter display will give you an indication of the relative resistance thru the wire (something like 0.3 ohms...........very small reading).
Proceed to the next wire until you find one where the meter doesn't change (tone or display readout). This then would be the wire that is bad.
Next step would be to either replace/repair this single wire or replace the complete wiring harness since you have just diagnosed the wiring harness as being "bad".
Hope this helps and post back what your results are.
Thanx,
KAMIKAZI