Thanks for the help Mike, I'll test with a 9V battery. Good idea! At least then I should be able to figure out if the LEDs are on the third wire or not. The wires don't have color coding - they are wrapped in clear wire coating and I can see the bare wires through the clear coating. The fan is not rated for moist environments, and I don't expect it to last forever, but for $7 I can replace it once a year if I need to.
It's going in the back wall of my stand to help move moisture out of the stand.