I sent an email to the site mentioned and I have to say I am impressed in getting a response so quickly..
From: Ian-HIDS4U [mailto:firstname.lastname@example.org]
Sent: 07 August 2005 12:12
To: Stuart & Zoe Hamilton
Subject: RE: HELP !!
The problem could be either the bulb or the ballast as the symptons of failure for both are the same. The simplest way is to swap bulbs round and see if the problem goes away.
Testing capacitors and other components souds a bit too much to me. If the ballast has failed it will need to be replaced, as only a few specialists would be able to mend them. They are full of chips and circuit boards inside.
I have supplied quite a few renault ballasts, normally Valeo, so its not unknown for them to go faulty.
I sell the original Philips and Osram bulbs for 39.99 on my site
If you need any more help or information please don't hesitate to contact us.
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I posted a copy of the email to answer the question on replacement bulbs and costs and also help this nice chap sell more ! Swapping bulbs over sounds like a sensible idea but to swap out a bulb you have to remove the front bumper and headlight units ( pain in the **** )
As for 500hr bulbs well the specifications are quite obviously aimed at the highest possible safety level due to the M.O. of the equipment but that's not bad for a car is it ?
Maybe my maths is all wrong but I could argue that 500hrs @ say 40mph average speed = 20,000 miles in the dark !
So being very generous that's 40,000 miles ( assuming you spend equal amounts of time driving day and night ) you can drive before ever changing a bulb..
PS:- I am a mechanical design engineer but I can't wire a plug all respect to the sparky types...