Brake lights stay on when running lights are on but work properly if the passenger blinker is switched on, the blinker does not it just stays on. Lights and blinker all work fine if running lights are turned off
What year truck?
Have you checked the brake light switch? And all the light’s grounds?
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In addition to @Mustangman 's recommendation to check grounds, check the sockets for corrosion.
I had a very weird one many years ago. A dual filament bulb burned out but the bad filament flipped over and spot welded itself to the other filament. I had some very strange interactions between the brake lights and turn signal. I forgot the sequence but it was like hitting the brakes caused the turn signal to come on partially. Real puzzle to figure out. Not sure why but when I finally looked at the bulb I saw the problem. I wish I kept the bulb or at least a picture of it.
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2003 Switch is ok i think break lights works fine when headlights off i check the grounds when i get off work thanks
Whet you describe sounds like a problem with the multi-function switch.
Tester
I replaced it first
From what you state about the lights working okay when the headlights are off indicates a problem with the battery to chassis grounding. Clean the connections to the battery and to the car chassis ground. When the headlights are ON it causes a significant voltage drop across the faulty and resistive connection due to the higher current needed by the headlights. That causes the lesser wattage lights to not work like they should.