What drain plug on the stern of an O'day 192? There is only the cockpit drain, unless a previous owner put something on your boat. The cockpit drain should not be plugged in any way, as it sits above the waterline. Plugging it will allow the cockpit to fill with water. You should crawl into the port lazarette and check that the hose from the cockpit to the transom is sound. If it leaks, you could get water inside the boat, either from the cockpit draining into the boat, or maybe from water coming in the transom hole from time to time.
As for the steaming light, off to the port side of the mast step, slightly behind, there should be a plug that the wires in the mast connect to. Mine was pretty well shot, so I used a 2 prong trailer style connector on mine. I just filled in the existing socket, which originally had a conical shaped rubber washer, with 3M 4000:
I do not believe in masthead anchor lights on small boats. So I just continue with the 2 conductor for the steaming light on the front of the mast as it came stock. It's only used at night when the motor is running, as per COLREGS. I installed a cigarette lighter socket next to my electric panel, so I can use a Caframo cabin fan, USB charger, or this light from Marine Beam, hoisted about 1/3 up on the main halyard tethered to the backstay for an anchor light.
https://store.marinebeam.com/utility-led-anchor-light-w-dusk-to-dawn-photocell-fx-ml-01/ (Tethering on a length of line allows the light to hang and not bang into anything.)
