Number Plate Light Driving Me Bonkers

[Sp3no82]

I have a 2008 A4 B7 Avant S-Line 2.0tdi 170 and I am being pestered with rear number plate light error on my dash, its intermittent and some journeys the warning beeps once and then comes back on, sometimes 10 times sometimes not at all.
I have changed the light units twice for 2 new ones that 100% work and are not faulty, I have removed the whole boot handle, cleaned all the contacts which were not corroded anyway and still I am getting this error. I am starting to think it might be the removable plastic bar that has the contacts on that is at fault. Can these be purchased separately, its always the driver side unit at fault the passenger side it fine.
Is there a fix or hack for this
cheers

 

[Baka]

It might be worth checking if the wiring loom into the boot hatch is in good condition. Sometimes the loom can get damaged from the constant opening and closing.

 

[Sp3no82]

How do I check this

 

[Baka]

Visually check and feel the loom where it goes into the hatch. Any splitting, heavy creases or looseness would indicate that it's not in the best condition.

Also turning your lights on, then playing with the loom and open and shut the boot. To see if the lamp flickers, dims or goes out.