GFCI isn't "appropriate" but rather required if the receptacle is within 6' of the sink or in an unfinished portion of the basement. The book Wiring Simplified is a great resource for homeowners. Home Depot carries it for under $10. Many jurisdictions allow homeowners to do their own work as long as the home isn't part of a multifamily dwelling. Check with your local code enforcement folks for rules in your location. This post was edited by mike_kaiser on Fri, Jan 4, 13 at 14:41

Given your answer to Greg's question I would not twist the two black wires together. Ideally, if you have access to the wiring for the fan, take some detailed pictures. Sounds to me like the fan is wired with two hot wires. If you can't get to the fan: (Goes without saying, turn the power off at the circuit panel when you do this.) Disconnect the two black wires from the top of the combo and put wire nuts on the exposed ends. Turn the power back on and see if the fan works with the other switch. If the fan works then you are good to go. At least 1 if not both of the black wires that are disconnected from the combo are likely live. If you have an electrical tester you can determine if one or both is live. Keep them capped and put them back in the box when you install the GFCI outlet.

The little outlet testers can't test GFCI without a ground. They leak a small amount of current from hot to ground which won't work without ground. As already suggested, the easiest and most effective way to test is use the TEST button on the GFCI. Randy: Actually to this day bathroom receptacles are allowed to be on circuits that serve only receptacles in one or more bathrooms. The other option is that a circuit may serve only outlets (receptacles and lighting, etc...) in a single bathroom. As Mike points out, adding GFCI's is cheap and easy if they are found to not be present.

NEC 680.23 requires that underwater luminaires more than 15V must be GFCI protected. The "typical" pool light at 110/115V requires GFCI protection. In a wet niche, they must also be mounted a minimum of 18" below the water surface Low voltage pool lighting at 12V does not require GFCI protection. If the low voltage light is set in a wet niche installation, the niche must be bonded inside and on the back side. Nicheless, low voltage, LED lights do not require grounding or bonding. Nor do they have a means to do so. Depending on the manufacturer, they utilize either 1.5" or 2" PVC pipe as a means for installation through a pool wall. They can be set close to the water surface. Generally 8"-10" below the water surface provides the best illumination. ALL the pool equipment since 2008 has to be GFCI protected. Prior to that, it was just pool lights. Bonding requirements have changed also. BONDING IS NOT THE SAME AS GROUNDING. A qualified and experienced electrician is the best person to review your pool set up.