I have a Merc coming in next week with a headlamp out, not had to change one yet so does anyone know if the bulbs and ballast can be tested and if so how. My understanding of the system (probably wrong) is that the ballast output is in the region of 8000 volt AC.

Hi Roger,
If you look at the bulb (don't touch the glass) it will be obvious if it has blown.
If you have a scope you can get some interesting waveforms from the wiring to the bulb and also using a inductive amps clamp.
Beware though initial volts to strike the arc are approx 18 to 27Kv then upto 130v AC pulsed at 400Hz to maintain the arc.
If you suspect a faulty ballast module you can substitute the one from the other side to confirm.

Hope this helps, I have lots of Bosch info on these if you need it.


Mark

is there any chance you can post this Bosch info on to this site so we can all benefit.

thanks
lee

Hi Lee,

The info I have are my course notes from a Bosch CAN bus/ body systems course I recently attended along with a few other UKAT members. And also a chapter in the Bosch automotive handbook which is a great source for reference. Both of which are prohibited from unauthorised reproduction, especially on an open forum.....

Sorry but I will try to help if you have any specific queries.

Cheers

Mark

Thanks Mark, I suspect we will be getting a lot more of these starting to come through now but at £70 a bulb is not something I will keep in stock.