All you wan't is simulating the bulb with a load resistor
Actually the computer is looking for a certain current drain produced by the bulbs running when you bturn the light switch on. The current is generated by all lamps.
A particular lamp has a wattage usually printed on the metal socket of the bulb or as indicated in the user manual. If you replace a normal bulb with an LED bulb you have way less current running than the computer likes to see. As an Alarm to indicate a defective Bulb, he turns the light in the instrument cluster on. You can not just put a 100 or 200 ohm resistor in paralell with the new LED bulb. You have to calculate the resistor based on the Wattage of the original bulb. If you have a 5 watt bulb that you like to replace, calculate the following
The Battery Voltage of the W140 is nominal 13 volts with running engine.
The calculation is as follows R = E 2 / P
Where R is the Resistor
E is the Voltage
and P is the Power in watts
Use the on line calculator here
http://www.the12volt.com/ohm/page2.asp to calculate the resistor In our case is 33 ohms and 5 watt for a 5 watt bulb.
You can do this calculation for any bulb that you like to replace with a LED bulb.
Now the computer does tolerate some variation due to variation of the Battery voltage and the fact that you have a little load coming from the LED. You could round the resistor value up by 20 to 25%, because resistors are only awailable with certain values. So select the one close to the value you need, but never smaller..rather bigger that you actually calculated.