Mercedes model R107 with automatic transmissions has a switch attached to the driver side of the transmission known as the Neutral Safety Switch (NSS) or in the electronic circuitry diagram in the manual as the Starter lockout and backup lamp switch. This video gives details of the function, removal and installation of this switch on a 1983 500SL. Access to this switch required loosening of a heat shield panel over a catalytic converter to provide a glimpse at the switch. However, most of the work was done by feel, while the car was supported on jack stands behind the front wheels.

Finally, note that the 500SL uses a slightly different NSS part number, being 0005455306 rather than the more common part for other SL models of 0005454906. The 500SL transmission is designed to start off in second gear in normal operation, unless the gear shift lever is in B, or first gear, or if the switch under the accelerator pedal is engages by flooring the pedal.