I ran the wires and mounted the tachometer. It works. There are two LEDs per 1000 RPMs. So beside the 0, the two LEDs indicate 0-499 and 500-999 RPMs.
I added a nob to the potentiometer, located at the bottom. This does indeed control the brightness of the LEDs.
I hooked the motor up to 12 volts and then 24 bolts. It revved somewhere between 2000 and 2500 RPMs. I heard no odd sounds from the motor. Given the way it sounded, I doubt I ever exceeded 5500 RPMs.