1. Which module do I need as a light switch for replacing my ceiling fan light switch? It's a simple switch but the WS12A switches can't handle the load I guess, they won't work.
Odd, the WS12A should work with incandescent fan light if the light controlling switch is separate from the fan motor control. Neither WS12A nor the WS467 will not work with CFL bulbs.
2. I have a light in my garage controlled by a WS12A switch and also a RR501 transceiver and a credit card remote to control it. I enter the garage from the back door to get in my car but the light switch is at the front so I use the remote to turn the light on/off in the mornings so I can see in there. I'd rather just have it motion activated, what do I need to do motion activation on this one light?
Any of the X10 "xxxxEye" motion sensors
3. I have a gas fireplace controlled by a light switch, what would I need to control this?
Crystal ball is broke, does the switch control 120V to the fireplace or is it a low voltage ignition control line. Low voltage controls are common and a "Universal Module" would be needed for that. The UM506 "Universal Module" requires a 120V outlet and gives you a contact closure. X10 does not make a "wall switch" to control low voltages. If the switch is controlling 120V a WS13A should work.
4. I have a few LED lights in my kitchen and they don't draw enough current for a WS12A to work with them. Which module would I need to control these?
LED lights are tough to control because the Appliance Module's local control circuit leaks enough electricity to keep LEDs lit. I use a Socket Rocket to control an LED rope light and it works well.
5. I have central air in my house and it's controlled by flicking a light switch on/off above the thermostat. Which module would I need to control this?
Well crystal ball is still broke. Assuming the switch is simply controlling the 24V AC line to the thermostat, again you would need the Universal Module since all other X10 switches are made to switch 120V or 240V. The UM506 "Universal Module" requires a 120V outlet and gives you a contact closure. X10 does not make a "wall switch" to control low voltages.