Riddle me this

[The Pox]

I have just noticed that when I open the tailgate the number plate lights come on very very dimly. I only noticed this tonight because it is dark. No other lights are on and the ignition is not either. It is not a major issue, but I just wonder if anyone else has noticed this or is it just on my Cali. You will not be able to see it in daylight as the glow is so dim. I would be fascinated if anyone can tell me why.

 

[EddieEagle]

This happened to my T5.1 after I changed the number plate bulbs from usual festoon bulbs to LED ones.
It seems to be a ‘feature’ of LED bulbs and now I’ve returned to the old ones.
Strange though, this doesn’t happen with the living area interior lights which are LED ….. I know this doesn’t explain why but just thought I’d share anyway.

 

[The Pox]

Interesting that it occurs on other vehicles. It would imply that there is some electrical drain. It does switch off after a minute or so but it is odd.

 

[dripster]

I thought so! I thought I was going mad and it was somehow light reflected off something, but I noticed this on our T6 Beach. Odd.

 

[The Pox]

The fact that is switches off after a minute or so if you close the tailgate, implies that there is a connection with the courtesy lights. However I am no electrician by any means.

 

[OGII]

Mentioned before.

Thread 'Rear number plate lights illuminate at low level when vehicle parked and rear door operated' https://vwcaliforniaclub.com/thread...-vehicle-parked-and-rear-door-operated.24105/

Low wattage led tend to fade slowly when switched off. The in van ones will be higher wattage and will "go off" straight away whereas the tiny ones used for number plate still have enough residual current that they show dimly for a while.

 

[dripster]

But no explanation? These come on without any other lights coming on. Is it some kind of residual current due to the unlatching mechanism? It's certainly not bright enough to illuminate anything. Just odd.

 

[OGII]

Maybe as a result of various lighting circuits activating for a while as a "at home path illumination" feature? The led then fade slowly after?

 

[vbk1975]

But no explanation? These come on without any other lights coming on. Is it some kind of residual current due to the unlatching mechanism? It's certainly not bright enough to illuminate anything. Just odd.

It is almost certainly a small current that is generated when the BCM is awake and the output diagnostics circuit is active (even although the light isn't activated). I suspect the original design was for a bulb which wouldn't react to such a low current.