Mb508 starts on the button but how do you stop it

[DEADSFO]

just taken delivery of a 1987 ex Nato mb 508 ambulance,the ignition key is a bit like bent nail it turns on the ignition then you start it on the start button,you can turn the ignition switch off but the engine keeps going ,I have been stopping it by turning the tick over control presumably starving it of fuel ,is this right or am I missing something

 

[Dieselman]

It should have a vacuum capsule on the top of the pump to stop the engine. Often either the capsule or the ignition valve leak, so there is no vacuum applied.

 

[DEADSFO]

It should have a vacuum capsule on the top of the pump to stop the engine. Often either the capsule or the ignition valve leak, so there is no vacuum applied.

this was a Nato reserve vehicle it has only done 1500 miles so most things should work,how is this vacuum capsule activated?