1999 Q45 Low Beam Head Lights

[GThreat]

Hi,

Both these low beam lights have stopped working at the same time, and I was wondering the easiest way to determine the cause? I pulled one off the bulbs out and just did a resistance check with no continuity shown through the filament. I also checked to see if I was getting voltage to the bulb, but was not sure what I should be getting. On the DC scale I got a very low (less than 1 volt) fluctuating reading.

So now I am very confused and would appreciate some help.

Many thanks,

Craig

[maxnix]

One of my bulbs failed recently, but before I daignosed it, I asked Joe if it could be a ballast. He said he had never seen one replaced.

[GThreat]

OK, I have this figured out now and thanks for your help.

The culprit was the HID relay, and I was able to prove this 100% by swapping identical relays around. Makes sense as it explains why both lights failed at the same time. Both burning out at the same time is remote.

I was not able to measure conductivity through the bulb as it contains 2 tungsten electrodes separated by Xenon gas. So with an ohm meter you see infinite resistance. It only conducts once you strike the arc using a high voltage.

Nice to have a simple cause and it allowed me to learn a bit more about the car.

Craig

[maxnix]

OK, I have this figured out now and thanks for your help.

The culprit was the HID relay, and I was able to prove this 100% by swapping identical relays around. Makes sense as it explains why both lights failed at the same time. Both burning out at the same time is remote.

Good work! I thought it unlikely also that both bulbs would fail unless there was a surge involved. But not impossible that they both failed as they had the same age.