Here is a quick guide on the necessary wiring for converting your E32/E34 to manual.
Part 1: Trans Program Error bypass
For this you'll be taking the #6 pin brown wire from the 6 pin blue connector and connecting that to the #10 pin Silver/brown wire from black 12 pin connector.
With these wires spliced together you will no longer have the Trans Program warning on the dash.
Part 2: Park/Neutral safety switch bypass
For this you will need to connect two wires on the 8 pin black connector. The pin #1 green/red wire to the pin #3 brown/black wire. With this done the car can now crank and start.
Part 3: Reverse light wiring
This step will require purchasing or making a simple EV1 connector harness from the Reverse switch on the transmission to the green/black wire and blue/yellow located on the same black 8 pin connector as before. This should be pins #6 & #7. See photos below.
Spliced the two wires to a female EV1 connector
Fasten this harness anyway that keeps it out of Guibo and moving parts
Also not pictured here is the oem grommet that would protect wiring.
Once plugged in reverse lights and mirror tilting function will work
With everything finished and tucked away your car should now start, have no related warnings, and have functioning reverse lights.