Oh man I already solved my problem. Best G3 problem ever!
Per the G3 service manual pdf, page 121 (front panel board):
"Replacement Note:
Power cable P4 connects to the front panel board."
I had no power cable plugged into the board. And the Mac works fine (other than the lack of LED lighting on the power button) without this plugged in. Interesting. I hadn't even noticed the board had a power plug slot. (I had the other two cables plugged in, however. Three cables total.)