A hard drive thermal sensor may be present on some models. If your logic board is missing the hard drive thermal sensor socket highlighted in red in the first picture, skip this step.

Pull the hard drive thermal sensor connector away from its socket on the logic board.

Pull this connector parallel to the face of the logic board toward the top edge of the iMac.

Use a spudger to pry the thermal sensor and adhesive off the hard drive and install it in the same location on the replacement drive.