interior light does not go out when the door closes

I have an old truck 1969 Ford F-100.  There is a button inside of the doorframe
that is connected to the interior cab dome light.  when you close the door the
button is pushed and the light goes out.  The problem I have is that the plastic
holding the button in place is cracked so the button gets pushed through the
hole that is holding it in place.  The button does not get pushed and the light
does not go off as if the door is not actually closed