I'm thinking of adding an SSD. I'm getting conflicting advice as to what to do with the sensor cable if swapping the mechanical drive for an SSD.

I think in these units, there is a sensor cable that runs to the mechanical drive, rather than a sensor probe stuck on the drive.

I've read that some short this cable, some put a resistor on it, even some saying mover the sensor from the optical to here. I have no idea if that is sound advice or not.

So it made me think, if I just do away with the mechanical drive entirely and unplug the sensor cable. And swap out the optical for an SSD. Will the iMac boot fine with this arrangement. And will it be smart enough to realise that there is no HDD plugged into, let's say the main slot, and therefore not care about fan control at all for that drive?

For context, apparently if the sensor cable is not tackled, the fans roar at 100% for this model and similar setups, when doing a swap of the mechanical for an SSD.

  • See this answer: apple.stackexchange.com/a/257938/119271
    – Allan
    Jan 7, 2020 at 10:44
  • @Allan , thanks I've read most of these posts. Not sure if that's even applicable for this model. The logic here is that a disk caddy would be the cheaper option. Second to shorting a cable. I could leave in the half dead mechanical, but it would be a waste of energy.
    – Progrock
    Jan 7, 2020 at 10:52
  • Applicable for all models that put the sensor in the drive (my 2012 and 2015 don't have it). Shorting the cable is not really a good idea because the sensor acts like a variable resistor and the SMC bases fan speed on the value it gets back. This is an easy fix and easy to open iMac. I'd get a good SSD, get the cable and you'll have new life in that iMac for a small amount of $$$
    – Allan
    Jan 7, 2020 at 11:07
  • @Allan , ta so here in the UK the OWC cable is listing around £30. A caddy <£10, and if a resistor is a better choice, I'd probably choose that route.
    – Progrock
    Jan 7, 2020 at 11:12
  • Resister or shorting the cable will end up sending incorrect values to the SMC. The sensor wasn't for the drive alone, but the ambient air around the drive as well. Just want you to have the full details when you make your decision.
    – Allan
    Jan 7, 2020 at 11:20

1 Answer 1


The usual result of removing the thermal sensor is roaring fans; I suspect that there's little reason for Apple to add some "if no drive, ignore sensor" logic, because Apple would want to replace the drive.

The best instructions for replacing components on your Mac can be found here: https://www.ifixit.com/Search?query=imac%202010

Remember that your iMac has a SATA II (3 Gbps) controller, so you're not going to see the full benefit of the SSD: though it will probably double your HDD's speed.

If your iMac had Thunderbolt, then I would have said avoid the hassle and use an external drive; but it is a 10-year-old Mac!

  • (It's only a decade old, a youngster. My desktop is at least 16 years, and my laptop 12!)
    – Progrock
    Jan 7, 2020 at 11:05

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