Chevrolet Repair: B/U Lights on 04 Duramax, lens assembly, backup lights

Question
The backup lights on my 04 CHev 2500HD 4x4 Duramax no longer work.  Have checked for, and found switching working at the park/neutral position switch on the left side of the tranny, but am unsure where to go from there.  the power is not getting to the lights.

Answer
HI JACOB,,,OK SO IF YOU KNOW THE SWITCH IS SENDING POWER TO THE REAR,NEXT STEP IS TO CK THE PLUG HARNESS IN THE REAR UNDER THE LEFT SIDE OF THE BED,MORE THEN LIKELY IF YOU UNPLUG THIS  HARNESS YOU WILL FIND GREEN INSIDE,, AS IN CORRODED..THIS IS A FAIRLY COMMON PROBLEM. ALSO CK FOR POWER THAT FEEDS THE REVERSE LIGHTS.[REMOVE A TAIL LIGHT AND CK THE COLOR WIRE THAT FEEDS THE REVERSE LIGHT SOCKET.THIS WILL BE THE SAME COLOR WIRE AT THE PLUG UNDER THE BED.].CLEAN IT UP IF YOU CAN OR CUT OUT THE BAD SECTION AND BUTT CONNECT IT WITH SHRINK TUBING TO PROTECT IT..IF THERE IS POWER TO THIS POINT THEN THE NEXT AREA IS THE PRINTED CIRCUIT IN THE TAIL LENS ASSEMBLY ITSELF. UNPLUG THE PRINTED CIRCUIT PLUG AND SEE IF THERE IS POWER TO THE REVERSE LIGHT SIDE OF THE CIRCUIT, THIS IS WHERE ALL THE LIGHTS GET PLUGGED INTO. IF SO THE CIRCUIT IS FAULTY. BUT BEING BOTH THE REVERESE LIGHTS ARE OUT I THINK YOU WILL FIND A PROBLEM IN THE WIRING HARNESS GOING TO THIS AREA.IAM SURE YOU HAVE CHECKED THE BULBS ????  YOU NEVER KNOW.JUST ASKING !!!! LET ME KNOW HOW THIS WORKS OUT FOR YOU AND GOOD LUCK,,,,TOM...