"Electronic" Fuse - rear number plate light

[wimphot]

One of the two rear number plate lights on my C200 - W203 Estate was blown. Decided to replace both.
On refitting: The the one that was blown (left) worked and the other (right) which was working previously now isn't. First thought- sold a dud (festoon type) - no both OK.
Earth - on both - OK but no +12v to non-working unit!
Checked fuse chart in drivers door FB - which states - Number Plate Lamp Fuse "electronic"
BUT Nowhere can I find any mention of how to deal with a "blown" electronic fuse.
Help - please

 

[wimphot]

At the MoT station I noticed they had swapped over - right working left not.
Picked it up ½ later (passed)
Both working!
Magic!

 

[Dickie Fix]

I noticed that one of the number plate lights had failed a couple of days before the MOT. No problem I thought, just change the festoon, but no, it's an LED with its own lens which fits in to the traditional festoon bulb holder. So that's £14 thank you very much. Oh, and interestingly, the bulb failure light didn't light.