Thermo fan one on constantly
Discussion
The TVR Speed-6 ECU Diagnostics Software User Manual (see the downloads page on MyTuscan.co.uk) has the following to say about the cooling fans and sensor faults (see p.4):
NB. The MyTuscan website also helpfully has a copy of the fuseboard layout:

TVR Speed-6 ECU Diagnostics Software User Manual said:
WATER TEMP
Water temperature is measured by the sensor located in the cylinder head. If the ECU detects a fault with this reading it will substitute a value of 95°C. The engine cooling fans are controlled by this temperature reading, and are turned on at 92°C, off at 88°C. Therefore under fault conditions the cooling fans will be turned on.
From your post it sounds as though you only have one fan that's stuck on, so based on the above I'd have thought that a sensor fault is unlikely since otherwise you would expect both fans to be permanently on. Have you checked the relays for both fans? If not, and if the second fan seems to be operating correctly (i.e. kicking in at higher temperatures), then could you try swapping the two relays around to see if the first fan then switches on/off correctly? If swapping the relays causes the fault to move to the other fan, then I'd say you've found the culprit.Water temperature is measured by the sensor located in the cylinder head. If the ECU detects a fault with this reading it will substitute a value of 95°C. The engine cooling fans are controlled by this temperature reading, and are turned on at 92°C, off at 88°C. Therefore under fault conditions the cooling fans will be turned on.
NB. The MyTuscan website also helpfully has a copy of the fuseboard layout:

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