Rear side light effected by interior light

[Remithevan]

HI, I've been trying to get to the bottom of this issue for my 2011 / Berlingo Enterprise van.

OSR Side light comes on randomly, and sometimes off again when van is locked up.
NSR Side light flickers, when drivers door is opened it turns off, When the passenger door is opened it stays on solid. 
When in the van and I turn on the interior cabin light it stays on steady.
Not sure its just the bulbs but heating control illumination not working.

I can't see ANY water ingress anywhere, at all! although there is some dampness under the carpets that are under the passenger seats. 

I have a haynes manual but cant for the life of me find where any earth points are.

As with all Vans there is quite a bit of condensation in the load bay roof when it is really cold. 

Could it be a bad earth? Battery? Comm unit or BSI?

( not done a BSi Reset yet )

I'm at a loss, getting to the point of wiring a new loom/switch just for rear sidelights!

[OMG]

Heater control illumination bulbs seem to be a thing that goes periodically. When I bought my van they weren’t working. 2 bulbs. Plenty of videos on u tube to help with replacement. Can’t help much with your other problems although checking earths and BSI reset are worth a go. Hopefully might cure problem!

[Remithevan]

Many thanks for that, found the videos on youtube. You cant point me in the direction of the earth points can you?