And in order to drive it high, it would need to have been set to OUTPUT, right? Something I didn't do.

I may have left the pin in INPUT or INPUT_PULLUP for longer than 300ms. would either of those have hurt it?

In other news:

I tried powering the Betz board with about 3.2v coming out of the "3v" pin on the arduino and into the "3v3" pin on the Betz board, with the 5v pin disconnected from the Betz board. Didn't solve the problem and the board was dark.