free wiring diagrams here
http://www.bbbind.com/free-tsb/ Enter vehicle info. Year , make , model an engine size. Under system click on lighting then under subsystem click on reverse lamps . Click the search button then the blue link . Looking at the diagram I see back up lamp PCB relay - non serviceable , soldered to the circuit board in the inside of the under hood fuse box. The relay is controlled by the BCM on command by the ECM - engine control module . The dashed line from the ECM - engine computer to the BCM , with the arrows is a serial data communication network . Having the BCM checked for code's would be the first place to start .
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