Is it ok to run only 1 lamp continuously on a 2 lamp, preheat ballast? If so, should it be run on the lead or lag side or does it even matter? Lastly, how can I tell which side is lead and which side is lag? Thanks for the answers!
Tom

Should be okay as you really have two ballasts, capacitors and a starting compensator in one ballast enclosure.

Lead side is the lamp that has the starter loop go through the ballast (yellow wires maybe? consult the wiring diagram). Lag side has a standard starter loop that does not go through the ballast.

I believe the lag side will give less trouble, but that's just a guess. You'll have to consider the other comments first.

Thanks for the feedback. On a preheat ballast with just a red and a blue wire, which one is the lag wire?

I dont know by color, but this can be checked with a multimeter. The Lead side contains a capacitor in series, if you measure the resistance from the Lead output to the line inputs, the multimeter is going to show rising resistance and then open circuit (or maybe some very high value) as the capacitor is charging up from the multimeter output. The Lag side is just coil, so you will see some relatively low resistance which does not change

If you can post a picture of the ballast wiring diagram, I could help you with the wire colours. Some ballasts deviate from the standard colours for wires hence the request for the picture.