How to test a Generator Cut Out

[Phil Gillespie]

My 38 PU is fitted with a 2 brush generator through the cut out then through an adjustable rheostat adjusted dependant upon load ie lights in use.
Know its not correct and should fit a voltage regulator for correct operation.
However how do you verify correct operation of cut out.Its the round Ford type which cannot be opened up.
Appreciate any advice on this one.
Phil NZ