Hope someone can confirm the diagnosis here.........

Fan failure (no action at all whatever) on my Xantia, and the blower is one
with the integral semiconductor speed control.
Voltage in from the loom (the big red wire on the multipole connector, I
assume) is 11.7V, but the output at the actual motor wire from the speed
control is under 8V all the time, regardless of the fan control setting on
the dash.
With the dashboard fan control on Max, switching the ignition on "kicks" the
fan slightly, but it never runs.
Bench testing the fan, it zips along merrily with 12V directly on the
terminals.
Looking at the assembly it does not look like it comes aparts easily -
replace the whole assembly?
How does the thermostatic control influence this unit, and is it misleading
me into thinking the problem is internal to the fan assembly?

TIA

Baffled (but not in the exhaust sense) Tone