You seem to have only one cooling fan, the earlier 406 had 2 and used the
circuit  shown on the web site I mentioned.
When air con is on you should have the fan running at slow speed to provide
cooling for the air con rad.
The relays you mention are used in conjunction with the resistors to change
the voltage applied to the fan an hence the speed. They are a notorious
problem, corrosion being the cause. You should be able  to prove the
resistors by
1) a resistive check with and OHM meter  with the connecting wires removed.
2) with a volt meter connected across the resistors when in circuit you
should see a voltage. You cannot get a volt drop across a resistor unless
the circuit is made and current is being drawn..
3) On my 406 disconnecting the thermostat that feeds the bitrol system
causes the fans to first run at slow speed and then at fast speed. This will
have the same affect as testing in 1 & 2 above but may give you more
confidence in the result
Mike.