Hi guys,

the high-rev-issue was fixed easily. It was just a dirty throttle valve that got stuck. After spraying it with brake cleaner, everything is now fine again.
Today I installed two more GMs. Unfortunately it brought no change at all.
I'm gonna focus now on finding that damned 50a fusible link.
I will also revisit the wiring loom under that carpet on the left side of the car. I'm sure the culprit must sit there.
I'll keep you updated about any results.

As usual, best regards from Germany!