After a transfer case rebuild to my 1992 300E, my 4Matic Failure Bulb would indicate an error code 10 after variable periods of time. Initially I reset it by disconnecting the battery for several minutes. Then I came across a reference noting that Pin 5 of the capped diagnostic connector behind the battery (actually visible as hole 5, which has a female contact below the black plastic surface of the connector) could be touched to Pin/hole 1 (which is ground) for control of the error codes and resetting the 4Matic system. Upon first encountering an error which turns on the 4Matic Failure Bulb on the instrument cluster, grounding Pin 5 for between 0.5 and 2 seconds will elicit flashing of the 4Matic failure light for the number of flashes at one second intervals corresponding with the type of failure detected. If Pin 5 is then grounded a second time, commencing about one second after "steady state" illumination has returned to the 4Matic Failure Light after a sequence of error flashes has finished, and this second period of grounding is maintained for at least 5-10 seconds, the 4Matic Failure Bulb will go out, and normal function of the 4Matic system will return, until the next occurrence of a detectable error condition. I led a wire from the wire going into Pin 5 of the diagnostic connector back into the passenger compartment, and whenever the 4Matic Failure Bulb came on which it did every few minutes to few days, I could reset it at will while driving. Eventually I discovered that the brake switch half which fed a switching signal to the 4Matic system had partially-conductive debris in it, causing the switch to open gradually, as if it were a potentiometer, rather than a switch. Cleaning out the switch and reassembling it gave me about a year of continuous error-free operation of the 4Matic system.