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Q: whats causing my brake lights to stay on when the vechicle is in the run postion on 2003 Dodge Ram 1500

I replaced my heater core and now the brake lights stay on when the truckmm is in the run position, but work great when the truck is turned off. My cruise control turns on but it does not engage when I hit the set button, my ABS lights come on, and it starts making a dinging noise and a light on the cluster comes on and says lamp out and theres no lamps out. I have removed dthe dash again and checked all the connections and reinstalled and itws still doing the same thing. All the other lights work like there suppose to even the third brake light. What tin the world could this be? Could the PCM be the problem?
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Have you checked the brake pedal switch? If that got out of adjustment during the heater core job that could account for all the symptoms with the exception of the 'lamp out' indicator. When brake pedal is at rest(released) the switch should be pushed in. If any doubt , try unplugging it to see if the brake lights go off. If the PCM sees the brakes 'on' (even though you're not stepping on the brakes) after a certain time/distance it will by default , disable the cruise control and ABS because it thinks there is a problem with the brake system. Please respond with results , so if that's not it , some other suggestions can be posted.
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