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2013 3.6 Performance Luxury
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Discussion Starter #1
My 2004 CTS has 105K miles on it. Saturday I went to have the annual state required safety inspection performed and it failed because the license plate lights are not working. They tried replacing the bulbs but said it did not fix the issue. Got the car home, one license plate bulb was burned and the other was good. Both white license plate bulb sockets where browned and a little 'charred' from what looks like an excess voltage situation (possibly from when the ECM recently went out). Replaced the bad bulb but neither bulb turned on. I then noticed the backup lights don't work either (key turned on, tranny shifted to R). Removed the harness that goes to the entire back panel and connected wires directly to a 12V battery (note: yellow wire is for license plate lights, green is for backup lights, white is for third brake lamp, black is ground). Hooking 12V directly to the male connector on this harness made all the lights work. Tested the female harness where it plugs into the other harness I just tested. Test light and voltmeter showed good on the yellow wire when the parking lamps were turned on. Test light and voltmeter showed good on the green wire when the car was put in reverse (with key on of course). When I plugged it all back up, the license plate lights still did not work, but ironically, when I turned off the parking lamps and put the car in reverse, the license plate lights came on. Obviously, the backup lights should have come on but did not, and instead, the license plate lights came on. I didn't find any fuses specific to any of these items. You can't buy just the back panel wiring harness, it is only sold with a complete new back panel ($450+). One thing I plan to try this week is make my own wires to bypass the rear panel harness and see what happens. Please help, I have 2 weeks to get this fixed and get the car back in for the final part of the safety inspection. If it takes longer than 2 weeks, I have to pay for another inspection ($40).

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Ha, just thought of something else. I open/close the trunk at least twice every day I drive the car, need to check the wires where they are routed near the trunk lid hinge.
 

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06 CTS Sport/Luxury package
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You already thought about what I wanted to suggested as I was reading this. By pass the plug that is on the trunk lid. You're not planing on taking the trunk off on a daily bases, so why not?

If the lights work after that, solder the factory wire to the new wire that you installed.

KOT
 

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2013 3.6 Performance Luxury
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Discussion Starter #3
Found the cause today. After realizing the trunk harness and sockets tested fine while the trunk was opened but the lights didn't work when the trunk was closed, I focused on the wiring that runs along the left trunk lid hinge. After peeling back the plastic loom, I discovered the ground (black) wire was broken. Installed a barrel connector, tested, and done!
 

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Bro I am going through the same shit. I just check if the was power going to positive side of socket and the test but probe light went on red. Tried it with multimeter and not reading so I know there is a break in the circuit now that you mention the wire wrapped in mesh I actually fixed my third brake bar due to a cut wire. Can’t remember the color. Thanks to reading this I know now where the problem surely is. First I thought it was my 2000 watt subs in a pro box flexing the the short out but now that I saw now voltage reading but power to the positive side I know the grounds are probably cut too. Going to solder then then put some x6000 or what ever that silicone around then to avoid future cuts.
 
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