Stiletto

Hi, Can anyone give me a clue to rad fans not working? 2004 WRX Turbo. Car and engine running smoothly, nothing sinister, no warning lights, driving fine, no major water loss, etc. I have checked the 20A fuses underbonnet fusebox, also that all relays are in place. Fitted a new engine temperature sensor, checked all the wiring & plugs, including earths to chassis - all fine. My wiring diagram shows 2 x Main Fans plus 2 x Sub fans and the colours on the diagram don't exactly match my car (!!) I have removed both fans and wired them to a seperate battery source - they do work on the bench. Also fitted new thermostat as a precaution. When I run the car at fast idle, temperature gauge normal for while, then starts to go just above half way on gauge, and I then have to switch off before it overheats. No sign of either fan working on either speed setting. Can you give me any ideas? Thanks, desperate for MOT re test and it has overheated during the first emission test, so aborted test.