Luckes2.0, my manual has only 20 pages in the 55-28 section.
Are you looking at a wiring diagram or a "location of components" picture of the car?
As far as I can see, they are kind of contradicting each other, but I think it is the wiring diagram that shows how things are really connected, and the "location of components" picture doesn't show the actual connections, just general locations of things and perhaps the looms...
(and I assume you mean 1997/1998, not 1977 and 1978
My chassis number is 603...., this means motronic version M2.10.4 and the updated key code solution, and there should be a g133a connector, according to the manual. So far everything I've looked at is correct according to the manual for the updated version (from chassis number 6023907), but I just can't find the g133a connector...
The orange-white cable from C10B to G99 continues to N77A, so I can't see how that is relevant when both N77A and G99 is disconnected, and I get the short to earth between G389 and G99 (pin 1).
See attached wiring diagrams that are the ones that should show how things are connected in my car.
I've attached the diagrams for the key code, motronics, air bag system and another one with the instrument cluster that shows G389 as well.
They show that the key code and airbag system go from G389 to G99, and that the motronic system go from G389 to G133a.
I can't find any indication that any connection goes from G389 directly to the instrument cluster, it also goes through G99.
So, as I see it I really need to find g133a, disconnect it, and see on what side of that connector the short to earth is located...