Bi xenon headlights

[benm]

I have a w212 eclass (pre facelift) with bi xenon lights. Recently notice the headlights were very poor and sure enough there was a message that right hand dipped beam faulty.
Checked relevant fuses and they were OK so naturally assumed the xenon lamp had blown after all they were originals and car now 11 years old.
Ordered new pair of xenon D1S lamps and spent a frustrating time fitting the right-side one only to find there was still no light . . . .

Read back actual values for right xenon headlight and supply voltage only 3.2v compared to 12v for left one. Further investigation traced the supply voltage to the thick yellow wire on the headlamp connector. Measuring directly at the connector also getting 3.2v although very occasionally flickering to 12v?
Am I correct in thinking the fault is not in the headlamp unit but what supplies it?
Where does the supply voltage come from?

 

[sonic]

I am sure this has been on before, worth a search.
There is a 12 volt feed to the ballast unit which lifts the voltage to the bulb to about 30,000 volts.
I think your fault is the ballast unit, where are you measuring this voltage. Before the ballast unit or after it?

 

[benm]

I'm measuring the voltage at the 14way connector that plugs into the back of the headlamp.
My understanding is the ballast is directly connected to the headlamp and has no external connections.

 

[sonic]

Then you have a problem with the 12 volt feed to the ballast unit. I would run a separate 12 volt feed from the battery direct to the ballast unit. The headlight should then work. If thats the case you need to follow the original 12 volt feed back. The only other thing to check is the earth to the ballast unit. Have you tried several earth points on the voltage check?

 

[Wighty]

What make bulbs ?
Does the left hand new bulb work ?

 

[benm]

Phillips bulbs. Left side is working fine.
It looks like the right headlamp supply voltage come from the front SAM which is located under the fuse box. Will read back SAM for error codes.

 

[Wighty]

Phillips bulbs. Left side is working fine.
It looks like the right headlamp supply voltage come from the front SAM which is located under the fuse box. Will read back SAM for error codes.

Swap the new bulbs over first ?
Edit…just noticed you had a warning that the right beam was faulty before the bulb change , so ignore me

 

[benm]

Unfortunately my code reader does not read the front SAM. Anyway traced wires back from headlamp connector to SAM and they were good.
Then out of curiosity disconnected good lhd headlamp and interestingly voltage at pin 6 now measured 3.3v. Thus I suspect the SAM must limit the voltage if it detects a fault?
I'm now fairly certain the problem lies with the rhd headlamp unit so tried another new bulb, admittedly not tested, and no difference. Is there a way to test the ballast?
Read back info on the xenon bulb and it has been operational for 110000 minutes, approx 2000hrs, which I believe is expected lifetime for the ballast?

 

[benm]

Today got round to swapping over the ballasts and the bad headlight now works so that is the issue.
An oem Hella ballast is circa £200 yet there are many cheaper makes available. Has anyone any positive experience of a different brand ballast or is it false economy?

 

[benm]

Replaced faulty ballast with used Mercedes ballast (Hella). Lights now working except ILS feature which automatically switches from low to main beam. I prefer to select main beam manually so not concerned.