2016 Mustang Convertible Tail light Issue

[Ninpop9]

I’ve got a 2016 Mustang and I’m chasing a weird rear lighting issue. The right taillight does not illuminate in DRL mode (light switch off), but everything else works perfectly — brake lights, turn signals, and both taillights function normally when the headlights are turned on. The left side behaves completely normal in all modes. I initially thought it was the taillight itself, but I swapped the left and right assemblies and the problem stayed on the right side, so I ruled that out.

I’ve also checked for codes and there are no lighting-related DTCs. I have aftermarket front switchback turn signals tied into the DRL circuit, so maybe this? Using a multimeter, I probed the PARK/running light wire at the taillight connector: the left (working) side shows proper voltage in DRL mode, but the right side only shows about 0.26V. Ground seems fine since brake and turn signals work without issue. At this point I’m thinking there’s a high-resistance break or damaged wire somewhere in the right-side running light circuit, possibly in the trunk harness near the hinge, but I haven’t opened it up yet. Curious if anyone has seen this before or can confirm the likely failure point before I start digging into the loom.

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[Adam the Lighting Guy]

European parking fog light? That's the only thing in terms of your current functionality I can think of.

 

[1 Wheel Drive]

I didn’t think the tail lights lit in DRL mode. Maybe the euro fog light suggestion is right.

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