Do the other instruments work? If not check the fuses, if the gas gauge only does not work it is usually the fuel tank sender unit that has failed but before condemning it the system needs to be properly checked out. For a wiring diagram, test procedures and instructions, 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