Peculiar electrical fault with the number plate light

[Fodens]

I have a fault with my number plate lights as both lights are out and the dashboard display is showing that the bulbs have failed. I have replaced the bulbs and cleaned the connection so I know that they are ok (and tried connecting a bulb directly to the connection pads to ensure that it is not the bulb holder).

I have measured 1.5v on the connection to the bulb holders and checked that the ground connection is good so this suggests that the wiring is ok (I presume that the 1.5v is part of the bulb health detection signal) so now suspect that this fault is a bit more significant.


I would be grateful for any information about this fault/ how to resolve it (especially as my MOT is due in a couple of days!).

Best regards

Steve

[Alan02]

Check for a short on the wiring to both lamps, thats + and - shorts. If there is, it maybe detected by the central control unit and it has turned them off for circuit protection.

[Fodens]

Hi Alan

Thank you for your reply. I have checked that there is not a short between the + and - terminals to each of the two number plate lights. I do not know if the two lights are wired in parallel but the tests on the wiring suggest that this is the case as the + terminal on each appeared to be connected to one another. I also did a test where I measured the volts between the terminals (on one side) with and without a bulb being present and the volts dropped to 0 when the bulb was in the circuit so I do not know if this suggests that the protection is removing the volts when the bulb is present or not.

Best regards

Steve

[Fodens]

In the end, the problem was solved by replacing both of the bulb holders. There is no logical explaination about how this solved the problem as the circuits were tested without the bulb holders and the lights would not come on so still a mystery.

Steve