I thought there was a low speed resistor for each fan, if your temp keeps going then they are bypassed and the high speed kicks in. Good way to check is take out temp sensor on stat then turn ignition on. Low speed setting should be triggered on both fans then high speed. Does sound like your low speed resistor(s) are buggered so jumping straight to high speed. Of course, I could be could be wrong! Has a previous owner bridged the pins already?
I had the rad out recently to change it. There has been no obvious tampering, two wires connected at the top of the fan shroud, and two wires connected at the middle. I assume its the bit at the top connected to two thinner wires that is the resistor?
Radiator (or heater) fan motors unlike wiper motors are almost always designed as single-speed motors for cheapness. To get the lower speed a second circuit (hence 2 relays) is used with a large resistance to drop the current. The trouble is the large resistance used often generates a lot of heat and eventually fails. Common on all cars. not just Alfas.
The trouble is the large resistance used often generates a lot of heat...
which is why they are located in the fan shroud, to be cooled by the air flow.
Same goes for the heater fan resistor packs.
In addition to the resistor(s), the resistor module also contains a thermal fuse which will blow if the resistor gets too hot, ie when a fan motor seizes.
Sometimes, if the resistor itself is ok, you can just solder in a new thermal fuse. But the resistors on the rad module usually fall apart from the attack of crud they have put up with flying through the rad...
To check all was well, I hooked the car up the FES. I tested the fan speeds and both worked properly. I then let the car come up to temperature and fan speed one did indeed kick in and regulated the temperature. It came in at 100 degrees C. Worked fine. Will see tomorrow if the car is just being Italian, or if the problem is now fixed!