James,
Sounds like you’re narrowing it down.
If the car is at rest (DZ), but the DPP1&2 are toggling on the VFC window on the RVU (which it sounds like your description), maybe; 1) the shielded cable (grounded on controller side only) is picking up a voltage induction, or 2) maybe the ground wire has broken from its terminal. I suppose a flakey inductor could be turning off and on in its failing state, but you’d be able to see that watching the cartop box DPP LED’s to prove it. Hmmm...good one.
I’m sure you know, but that cable should not be anywhere near cab lighting circuits or any high voltage wiring runs.
We’lll be watching for your fix!
