Step back.

Step 1 - Do the sending unit unplug test.
Step 2 - Post the result.

The result may or may not indicate a short.

You need to know the test result before discussing a short and where it may be located --> there may not be a short as the unplug test was not done correctly. However, detecting a short in a wire would generally mean the bare wire is contacting a metal ground (break in wire insulation).

 

Yes, I understand I need to repeat Step 1, and unplug the correct connector. I was just trying to understand how this works.
Thank you.

 

I unplugged this connector, turned the ignition switch to ON II, but the fuel gauge is still on full.

 

Now do the short test on the Yel/Blk wire.

 

Unplug the harness from the cluster and then do a continuity test from the Yel/Blk pin to any metal around it, like the metal that the seat rests on? Sorry, this will be my first continuity test on a car...

 

Yes, continuity to body ground test. You can use the black ground wire in the 3P connector as ground.

 

That makes a lot more sense.

Does it matter if I do this on the cluster end of the wire or on the sending unit's side?

 

No. Either or both should be fine.

 

Will certainly be cleaner and less sticky on the cluster side...

 

If you pull the cluster, first check if the wire is shorted to ground, should be open circuit. Then plug the tank back in and measure resistance from the wire at the cluster plug to ground again, testing all the way through the circuit. Depending on how much gas is in the tank, it should be somewhere between about zero ohms (tank full) and 40 ohms (tank empty). If that checks out, the cluster must be bad.