Sounds like the switch is broken and needs to be replaced. In most cases the steering wheel needs to be marked and removed (after disabling the air bag if so equipped). The switch is most likely only available from the dealer, perhaps try www.rockauto.com. Autozone have some popular workshop manuals for free on line once you register (for free) on their website http://bit.ly/autozone_repair_info. There is also a company that independent auto repair shops buy their information from that the same information inexpensively to do it yourselfers. The information is year make and model specific repair procedures, service bulletins, component locations, wiring diagrams ect.... Alldata is very easy to navigate http://bit.ly/AllData_Repair_Manuals_Online
The labor to replace the switch is probably one hour labor.