I found this online and did what it recommended and I got all lights - all good. But I don't know what it means. In other words, what is causing this ...

Verify Illumination (Optional): If you find voltage at socket #5, you can jump (connect) socket #5 to socket #8 to see if the instrument cluster bulbs illuminate. This helps confirm the rest of the circuit is functional.

Afterwards, shunting the rheostat still resulted in no illumination. So, with that being said, could it be the rheostat or did I foul something else up? Trying to be thorough before I jump and buy another rheostat while that's not the problem.