Used car, internal dome light 12866 philips 12v 10w not working

[matrixofdynamism]

So this is about the internal light of my new used car. It does not work.

I used my fluke meter to measure the voltage on the terminals of the bulb socket in the car interior. With the bulb inside the socket, I get 0V. With the bulb removed I get 4.3V. The bulb itself is a "12866 philips 12v 10w". I have connected the bulb to my bench power supply and powered it from it. The bulb is not defective. I noticed that perhaps because it draws a lot of current, the voltage on the power supply output drops.

I had expected that perhaps there is a problem with the fuse as I have come across on the internet. But if the problem was with the fuse, then I would not expect any voltage on the car internal bulb socket with the bulb removed where I get 4.3V. What could be the problem?

[SeanB]

Most interior lights have an ability to be turned on with the doors closed. If it does then the door switches are faulty or disconnected. Have you tried opening all doors to see if it is not just the one door? Have you looked in the owner's manual and checked the interior light fuse, which often is shared with the internal accessory socket/ cigarette lighter circuit, and a blown fuse will lead to this, especially if it has just left a conductive metal vapour that will still allow voltage into the high impedance of the meter but not the low resistance of the bulb.

[SL4P]

Consider also that many cars in the last 15 years have had delayed/dimming interior lights.
Look at the bulb voltage with a scope rather than a DMM to see if there is a waveform rather than a simple voltage.
Look for the PWM controller under the dash, or in newer cars, it may be part of the body computer.