The ASR light in my 1990 500SL (W129) comes on occasionally while driving, with the associated heavy throttle and reduced engine power. The only way to have the light go out is to stop the car and stop the engine. On restarting, everything is back to normal, and the light does not come on any more for a while. Today this happened 3 times, which was annoying. Because I have found difficulty obtaining maintenance manuals and wiring diagrams for 500SL's, I am requesting help from anyone with knowledge about repairing ASR problems.

Does anyone know where to obtain a maintenance manual?
For other cars I own from other car marques, enthusiasts have
provided comprehensive manuals free over the internet
downloaded from their website. Does anyone know if this is
available for W129 SL cars?