were is the vacuum switch on 99 blazer for the 4x4

ive seen the pic of the vacuum switch for the actuator,ive been told were it roughly is center on the firewall behind the distributor,but i could use a pic for sure.i looked and i just dont see it im not blind hehe,do all 99 lazer have this,i traced the vac line fron the actuator under the bat tray and it goes behind the engine and down and continues on the the tranny ,sooo again do all 99 blazer electronic tc have this vac switch could it be located somewere else ty.