The start inhibitor swith screws into the topof the BW-35 just above the point where the shift linkage attaches to the side of the transmission. It can be changed and adjusted (by screwing in and out) from underneath the car. The switch on mine (before I converted to an M-41) was subject to frequent failure because the reverse lights draw too much amperage for the switch. The last time I changed it, I wired the backup lights to a dash-mounted switch and had no more ;trouble. The switch activates a relay (Start inhibitor relay) on the left side of the engine compartment which can be checked by shorting around it. In manual transmission cars, this same relay actuates the backup lights.