I can confirm the OWC thermal sensor cable is not needed for HDD to SSD upgrade. I successfully upgraded my 2017 5k iMac fusion drive’s HDD to WD blue 2TB SATA3 ssd without it and the fans speeds don’t ramp up at all. Anyhow thanks for your guides Ifixit on how to DIY. I successfully upgraded my 128gb NVME to a 1TB NVME and to a SATA3 ssd for storage. Transfer speeds are insane and my boot up time now only takes 12 seconds compared to 32 seconds previously. I also upgraded my cpu from the i5-7600k to the i7-7700k. My 2017 5k iMac is blazing fast now. Thanks again ifixit.