[Vwdiesel] Continued taillight trouble

[Kneale Brownson]

Chasing down the whatever causing my weird taillight performance:
 
I've cleaned up all the trunk grounds that a couple years ago caused a similar symptom with the tail lights without getting the solution I got then.  
 
I've determined there is continuity between ground and the contacts of the bulb holders where the power goes to the bulb, as well as between the ground on the bulb holder and the power contacts.
 
What happens:
 
With the brake pedal depressed, both filaments of the tail light bulb light up, along with the bulb in the yellow turnsignal section at the rear and the yellow lights in the front of the bumper.
 
With the pedal still depressed and the light switch activated,  both tail/brake bulb filaments stay on, but the rear yellow goes off and the front side marker comes on.
 
With the pedal still depressed and the key and lite switch on, when using either flasher activated, both tail/brake light filaments work and the yellows flash front and rear.  I get a faint glowing of the green arrows on the instrument cluster between flasher uses.
 
With the brake pedal released, and key and lite switch on, rear brake/tail lights have just one filament lighted and rear yellows go off.   Dash arrows go off too.
 
With the pedal reseased, the key off and the lite switch on,  still one filament in the brake/tail bulb and front yellow lites.
 
Any suggestions to where the continuity between the grounds and the power contacts of the bulb holders comes from?
 
I do have a trailer lights setup with its own power supply installed.  It was installed after solving the grounds issue a couple years ago and worked fine with the trailer until the current issue developed.