Basically, if the shut off valve gets vacuum, the engine will stop. No vacuum the engine keeps running. When the switch is in pos 2, the vacuum to the shut off valve is blocked, so no vacuum. When you shut the car off (pos 0), the block is removed an vacuum is allowed to reach the shut off valve, which then shuts down the engine.

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

99 W210 E300 Turbo Diesel, chipped, DPF/Converter Delete. Still needs EGR Delete, 232K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Gone and still missed...1982 w123 300D, 1991 w124 300D