Your description of the systen is correct, power is ignition switched via fuse B, thermostats are on the back of the heated glass.
Only real way to check operation is to wait until a cold morning when there is mist on the glass then start up and see it if disappears.
'08 Chrysler 300CRD (MB OM 642 engine)
'95 E220 estate
'89 230TE (R.I.P.)