You would need to start trouble shooting the wiring diagram for the top. There is 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
Autozone have some popular workshop manuals for free on line once you register (for free) on their website http://bit.ly/autozone_repair_info.
and get an online repair manual subscription.
I just looked at Alldata they have very good theory of operation and trouble shooting ideas.