There is a factory way to shut off ASR so the car can be run on dyno rollers Have a look through these threads, I think there is a schematic in there somewhere. The Rentech bypass system is a $$ way of putting the system into test mode. From what I recall, it involves grounding a wire each time the car is started.

http://www.peachparts.com/shopforum/sl-forum/130085-1991-500sl-asr-light-disable-traction-control.html


http://www.peachparts.com/shopforum/performance-paddock/55692-diy-asr-defeat-switch-18.html