Ok, plug "C" has two wires in it
- Red/Yellow carries power to the Brake Controller.
- Red/Dark Green carries power to the Transmission Control module and Shift Lever Assembly (Which do not exist in a manual transmission car.)

I think they had a bad traction control relay and did the dumb thing - wired in a relay instead of putting in a new RCM. If you restore the wiring to the RCM to what it was from factory, a new RCM should work fine.
But I can't say for sure, so many black wires make it confusing.