usually a on off switch on the top of the dash in the center,,at least on the cars, electric conversions are available from new port engeering..they will be 12 volt not 6 volt nos vacuum motors are on e bay

1966 barracuda prostreeter super charged 340(SOLD)
1940 dodge coupe 241 hemi street rod
2014 ram express hemi 4x4 dailey driver
2015 cherokee
2013 R/T classic