Hi Shogun,
My battery is in the engine bay. I also tried looking for the fusible link under the rear seat where the battery would be located but could not find anything.
You are correct, the blue wire was installed by my dad and me. It connects two wires that were used by the workshop where the car was (without success) being diagnosed after getting towed from my house be the ADAC (German Drivers Club).
The mechanics at the workshop used the wires to bypass the starter in order to test if it was still working.
My dad and me connected these two wires and installed a button switch which could be used to bypass the starter on demand.
Why did we committ such a weird act of Frankenstein-experiments, you may wonder. Well, the answer is simple: Before we found out that the car starts fine after pulling the GM, we were looking for an improvised way to get it running. And a switch is much nicer than bypassing the two wires with an additional wire. I'm 100% sure that this little "feature" is not messing with the car. All problems were there before and nothing changed after we did install the switch.
Anyway, my hope is on the two new GMs that I ordered from ebay. I also thought about replacing the K15 relay which controlls the power given to the GM and RM. I read this on this website: http://www.ah525i24ve34.at/HTML_ah52...ktrik_zke.html
Thank you and have a nice sunday.
As usual, best regarsd from Germany.