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I thought it was because the tail light was bad so I replaced it and the same LED strip was out on the replacement light, which points to something to do with the connection. From what I saw there was just one connector to the light so I'm not sure where the problem could be.

I tested the reverse fog light and the reverse gear lights on the tail light and they worked fine, but after a few weeks the reverse gear light would work sometimes and not others (and later failing altogether and causing a warning on the dash to come up), which again points to something other than the light itself. Anyone have an idea of what I can check/replace to fix it?

The car is a 2015 Audi S3 (8V) sedan. Pictures of the lights below for more reference.

Left light with malfunctioning LED enter image description here

Left light with reverse fog light illuminated to show the light isn't completely dead enter image description here

Right light with functioning LED enter image description here

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Since this lamp is mounted on the boot/trunk and it started out as an intermittent fault, it would suspect that the wires that take the power to the lamp have broken.

The wires pass through a rubber sleeve from the car body to the boot/trunk and flex each time the boot/trunk is opened and closed.

I would start by finding the rubber sleeve which will be near the hinge and with the lights on, bend it with your hand to see if you can get the wires to temporarily reconnect and the lights come on.

After that, it would be a matter of having to identify which of the wires are for the faulty lamps and the trace the wires back to find the fault using a multimeter. You may be able to replace the individual wires or replace the boot/trunk wiring harness.

Did the connector that plugged onto the lamp look clean and dry with no corrosion?

There is also the possibility that there is a connector on the car body side of the harness that has been getting wet and is corroded, so that would be worth checking.

You could also try swapping both back lights over temporarily to make sure that the fault persists on the same side of the car.

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  • I took a quick look and the wires are completely hidden behind panels and the metal hinge doesn't leave any wires exposed. I'll have to remove the paneling to get at the wires, which I'll try to do this weekend. Thanks for the tip.
    – Pedram
    Mar 17 at 6:38
  • Sorry it took so long to reply, but I removed the paneling in the trunk and leading to the back seat so I could follow the wires going from the light (until it went under the back seat area), and I didn't see anything wet or corroded. The connector to the light also looked like it was in good shape. I tried switching the right and left lights, and the light from the right side didn't turn on at all when I switched it over to the left side. Also, the radar at the back for the blind spot monitoring recently stopped working, so it seems like more electrical stuff is slowly failing in the back.
    – Pedram
    Mar 31 at 4:27
  • Did you check the length of cable where it passes from the body to the trunk lid where all the flexing of the cable takes place. It is likely that the wires have snapped internally there.
    – HandyHowie
    Mar 31 at 5:45
  • I did look at it and it looked fine from the outside, but I didn't open up the wiring to examine in detail. Photos here: imgur.com/a/ruU3vWT It's possible that there's a problem inside the wiring's shielding. At this point I think it's beyond my ability to fix so I'm going to take it to a mechanic friend who is good with electrical issues. I'll report back what he ends up finding.
    – Pedram
    Apr 4 at 19:56
  • Looks like it was broken wires. I took it to a friend and he sliced open the sheath covering the wiring in the trunk and found a bunch of broken wires. See pic here: imgur.com/a/C2HvBLJ Thanks for the tips on going in the right direction!
    – Pedram
    Apr 6 at 22:56

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