Anyone come across this problem. Xenon headlights come on ok and after around 20 minutes one of the headlights ( near side) goes off for about 5 minutes then comes back on for 5 minutes and so on. Dealer said put new set on for 750 GBP.
anyone got any suggestions to try and repair this in my workshop?

 

My 06 STR had an HID that would come on initially and then turn off. Not sure if it came on again and went off again during my drive but i suspect it might have. I found a bad igniter socket where it looks like some tried to replace the bulb without removing the the assembly and due to the impossibility of installing a bulb with the assembly on the car, they screwed up and it wasnt installed right and it melted the socket. IItried replacing the bulb while installed and I found the bulb and igniter just floating around in there. And I tried for a long time to get it in but found it was impossible to align the bulb in the assembly and getting the spring clip on the igniter and installing the connector while reaching thru the small opening behind the installed assembly.

So I took off the bumper cover and removed the assembly and I replace the bulb, the igniter with the melted socket, the HID ballast (for good measure) and the HID relay because it may have been overloaded due to the **** poor job a previous mechanic or owner attempted.

Its been working ever since!

 

Pics

I also found a very corroded connector behind the MISSING front drivers side wheel well liner so I replaced that too. THE CAR HAD NO LINER ON THE DRIVERS SIDE AND WAS MISSING THE BELLY PAN AND (sorry for caps just woke up and cant see my phone) missing the radiator cover piece and the two plastic trim inserts for the lower oil coolers and all that let water in and corrode various connectors

took a while to diagnose but its fixed now! Rain water and connectors dont mix

 

I'd start with replacing both "bulbs". Look for the D1S type. These have become surprisingly affordable over time (check eBay, Amazon). Replacing them is pretty straightforward. I believe it is even described in the owner's manual. To my knowledge, these lose some brightness over time, so expect an improvement with new parts. There are several options as to the color. I went with stock (a bit more yellow), but you can go more towards white and even slightly blue.

Next step would be to replace the "balast" (more of a power supply, really). These used to be quite expensive but have come down in price as well. Stock is Valeo. If you have the time, try and swap these left-to-right and see if the problem moves as well.

Of course, nothing replaces a visual inspection. Check the back of the light for that rubber boot. Check the metal clip and electrical connector. Check for water damage, signs of arcing, etc. Access is through a cutout in the wheel well liner. Make sure you steer your tires all the way to the end to free some space, no need to take the tire off. You know what to do...

Best of luck, keep us posted.