Brake Lights
 

2015 GMC Sierra. Rear brake lights on all the time along with signals on solid even with key out and truck off. 3rd brake light works normally. Any idea where I can star

Is the emergency flasher on?

No they are off. the 3rd brake light works normally

Is it had a trailer electrical hitch installed?

Factory on the trailer hitch and plug

what's the brake light switch at the brake pedal look like? these are a cheap/easy replacement. or was on my 09 when the cruise stopped working. maybe the switch is shorted on.

Did you unlock your doors with the key fob? There are two sets of lights that come on when you do that and only go off when you either start the ignition or re-lock the doors with the key fob. It's a safety feature for when you're parked in a dark alley somewhere. The rear red lights are easily mistaken for brake lights.