Let's cut through it.
You don't need the cable on a 2009–10 iMac if installing an SSD. I'll tell you Apple's dirty little secret on these: Take the old sensor, strip a few inches of bare wire and short circuit it. Tape it up. You can disconnect to do this but you must plug it back in. An open circuit will make the fans roar full blast.
If the OWC sensor makes you feel more confident, by all means put it in. My 2010 has one.
Oh, it definitely has one.
Do not bother with SMART stats on a 2010. It will waste your time and tell you what everyone knows: The drive should be thrown away. It went south a long time ago. 100% of the many that I have replaced in school computers are bad.
Do not buy that overpriced, underperforming SSD from OWC. Get one of these—whatever size fits your needs and budget:
https://www.amazon.com/Blue-NAND-500GB-SSD-WDS500G2B0A/dp/B073SBRHH6/ref=sr_1_3?crid=3MFAAV9YGXW0O&keywords=wd+blue+3d+nand+500gb+pc+ssd&qid=1561590038&s=electronics&sprefix=wd+blue,electronics,198&sr=1-3&th=1
This adapter is not absolutely necessary but it makes your life easier
https://www.amazon.com/Fenlink-Internal-Hard-Drive-Converter/dp/B01ELRRKW8/ref=sr_1_9?crid=1UI5KWO4VH963&keywords=2.5+to+3.5+adapter&qid=1561590131&s=electronics&sprefix=2.5+3.5+adapter,electronics,206&sr=1-9
Get a CR2032 battery for the NV RAM at any drug, grocery or hardware store. The original is a high-heat BR2032 but you're getting rid of the major heat source in this. There is a minute or two more to replace the drive while going after the battery. The OWC toolkit with the suction cups is good and iFixIt has tools, too. The SSD is a piece of cake but the battery requires the motherboard to come out on a 2009–10 iMac (both sizes). Here are the directions. It's long past time and you don't want to go back in for this.
https://www.ifixit.com/Guide/iMac+Intel+21.5-Inch+EMC+2389+PRAM+Battery+Replacement/6292
At this point, I'm going to recommend doing this yourself only if you're really handy and follow directions well. Otherwise, most techs I know charge $75 or so for labor (doesn't take them long either).
If going after the battery, here's a tip: Take some white-out and mark all board and in-line connectors so that you know the orientation when reassembling them. They're tiny and easy to jam in the wrong direction for the inexperienced.
