Why did the engine wiring harness replacment fix so many seemingly unrelated issues?

[Ascension]

Before I did the upper harness on my 420 I had seemingly random and unrelated issues like one side of the stereo dropping in and out and the intermittent function on the wipers just quitting. Replaced the upper engine harness and suddenly all these electrical gremlins

in the other seemingly unrelated systems just vanished .
These systems are not interconnected that I can tell so