Hi guys, have this very anoying problem with my a3, i noticed that my number plate lights wasnt working so i bought a set of new ones, fitted and nothing, i thought maybe its the contacts so cleaned them and still nothing, so i measures the power on them contacts and also connector under the trim and its 0.73 instead of 12, any idea what the hell is that and how to fix this problem?

Have you checked the earth wire/connection as well? 

If you have a poor earth then the voltage will read low also. try a substitute earth lead to test it first and then replace if necessary.

Hi Trevor, thanks for your reply, ive checked the earth also and its everything bang on and for no reason one of the lights started working now but other one still not working, this is doing my head :D

Hello Martynas,

Always difficult to advise on electrical problems at a distance. As Trevor says, earth issues can be a problem, but you now seem to have discounted that as the reason. These lights are usually pretty basic in their electrical connection and although it's great to be able to fix these issues yourself, very often a half an hour time with an auto electrician is money worth spent, unless you have a good meter and know your way around with it.

One possible cause can be broken/partially broken wires in the wiring harness which sometimes connects from the body/ roof area into the boot lid - generally in a fluted rubber covering. You will find this section of harness flexes every time the boot is raised and gets brittle over time. 

Kind regards,

Gareth.

Just for anyone in the future the bulbs won't work until you change them then turn the lights and ignition off and turn back on the system is can bus and supplies a small voltage on bulb check then cuts out if it detects a fault if you have 0.6v across the pins then it is working