Sam, Sam, Sam,
You used to be such a pleasant poster. I FEEL your frustration!
I too had "grounding issues". Your ground connections do not look right. Like somebody spliced it in 'after the fact'. However, they could be factory. My stereo had similar ground problems. Always a short - until I ran my OWN GROUND. Then, and only then, did the stereo work. I too was fed up at that point and merely replaced the WHOLE ENCHILADA.
I am not suggesting to pull everything out but I would certainly start by re-running those questionable ground wires and ensuring they are properly grounded and without fault.
Another thought, have you replaced your ignition switch and have a fresh battery?
If that doesn't work - find a Jaguar mechanic…half their problems are electrical.