Chosen Solution
I recently disassembled my 21.5’ iMac and upgraded my 500GB WD hard drive to a 1 TB WD Caviar Black. I made the mistake of not documenting the way the temperature sensing cable was connected and oriented. On my 1st attempt the fan would always run. On my 2nd attempt the fan would not come on. Please help me figure out how this cable is connected. There are 8 pins and only a 6 slotted connector.
With the underside (circuit board side) of the drive facing you, leave the 2 leftmost pins exposed. Good job on not switching hard drive companies! You would’ve needed a new temperature sensor cable if you had switched brands. Good luck!
