The data sheet it came with was for an HG25504 and the documentation doesn't really cover initialization of the LCD (if it does I'm not understanding it).
I am also unable to get the screen to display anything.
You may have better luck with the datasheet for the controller which I believe is an SED1330. Certainly the quality of the printing will be better than the one I found for the HG25504 at All Electronics.
Does the HG25504 handle pins 1 - 17 and the SED1330 controls 18-31?
I believe that HG25504 may identifiy the LCD module (the printed circuit board with the display, controller, and other components) whereas SED1330 identifies the controller chip (one of the epoxy blobs on the pc board). You would need a decent datasheet for the HG25504 to figure out pins 18 - 31.
You have to supply a variable negative voltage to this pin and adjust it for a good display.
...and this was with just a potentiometer hooked up to Vo...
... or does that indicate that it will be fine without one?
A potentiometer has three terminals, where were the other two connected?
It's not likely since the data sheet shows a typical value of VO to be -10.1 Volts if VDD = +5 V.
...and just want to figure out how to make it work.