I'll bet your car needs the whole upper wiring harness ....M119 motor, right?
Check the insulation, or lack thereof, on the harness. That vintage MB used biodegradeable wiring covers made from vegetables and your lucky if you've gone this long on the original wiring. Around $500 for a new harness that you can put on yourself (maybe 20 connectors) if you take your time.
Rule that out first before changing out any sensors/parts IMO. A few cheap parts to switch out regardless is the brake stop lamp switch and the kick-down switch under the gas pedal (around $20-25 each). Those can also cause the 'LH' mode to come up.
Of course, checking the fault codes thru the CAN is a must also. Good luck. Nice cars them old S-class but like most any 10 year old plus car....$$$ to maintain.
