I have a similar problem but for a different reason.
I have a 21 inch Imac and i recently changed the 500g HD for a 1G.
In the procedure it noted to be aware of the fan control connector position on the HD, and that installing reverse would cause it to run on high. I think i read it wrong however.....i put it back in the original orientation and now my fan is on high all the time.
Does it make sense to have to reverse the fan cable orientation when changing drives?
OR - am i missing the point all together....i am thinking the thermal sensor is the 4 pin connector on the hard drive next to the sata and power connectors? Are there versions of drives out there where there are more than 4 pins?
Step 10 — Hard Drive ¶
Before disconnecting the thermal sensor cable, take note of its orientation. It is extremely important to reinstall the connector reversed from the current orientation so the fans will not run at full speed.
Disconnect the thermal sensor by pulling its connector away from the side of the hard drive.
During reassembly, be sure that the thermal sensor connector is connected to set of pins closest to the SATA connectors. If the fans spin at full speed, reverse the connector's position