Taillight not coming on with headlights?

[southwestheat]

A weird issue popped up with my '21 GT. When the headlights are on, the driver's taillight doesn't come on. But it will work correctly if the turn signal is used or the brakes are applied.

At the same time the above began, the driver's side front parking (yellow) light doesn't come on with the headlights, but works fine when the turn signal is on.

I'll have to take it to the dealer but would be interested if someone has any ideas about what this could be? It'd be nice to help guide them early on given how slow service departments are...

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[Cobra Jet]

First, disconnect the wiring harness from each assembly. Then plug back in and see if that corrected the situation.

If it did not correct the situation, it’s possibly a BCM issue for the lights, or there’s an issue in one or more harnesses. Have you checked all grounds to ensure they are secure and tight to their mounting points?

 

[coz0502]

Replace the driver's side front parking light and see if that resolves it before taking it to the dealer.

My passenger side front parking/signal light burnt out and the passenger taillight stopped working. It was a couple years ago so I don't remember exactly, but if I remember correctly, the brake and signal light worked but the running light did not on the rear taillight. Once I replaced the burnt out front signal light everything worked properly again. It may have take a few mins after replacing for the rear to start working again. I may have even pulled the battery for 15 or mins or so to reset everything. Good luck!

 

[Mike Pfeifer]

If you’re taking it to the dealer, don’t mess with it, just show them what it’s doing. Everything is LED on this car, with the exception of the reverse light and rear side markers, so nothing to change there. It sounds like a control module issue with park lights / driving lights on one side only.

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