passat estate 2013 dim high level light

[Biglegs]

when parking the car at night i have noticed that the rear high level brake light is still on . have taken the panel off and checked all connections and all are ok , i have noticed that when the boot is opened then the light goes out . holding the tailgate in place and closing the latch will bring the light back on but when it is opened with the tailgate still static in the same place the light comes back on , this was done to prove no break in the wire to the boot lid , all the earthing points were checked and cleaned before re installing and still no effect ..

so now top light is disconnected to ensure the battery does not run flat on me

any advice on things to try would be great or point me to a post where this has happened before
Marty