2014 Dodge Ram 1500 U0143 Fault: No Rear Turn Signals, Brake Light Dimming, and Communication Loss with Multi-Purpose Module

My 2014 Dodge Ram 1500 has developed a fault where the rear turn signals do not function at all. Only the front turn signal activates when I press the brake and engage the turn signal. Additionally, when braking, the brake light dims significantly—this is consistent with the issue. The flasher unit operates normally, and I have already replaced both the turn signal bulb and the light switch without resolving the problem. Notably, the light switch now remains in a constant 'on' position, indicating an automatic stay-on condition. The vehicle has triggered Diagnostic Trouble Code U0143, which indicates a loss of communication with the Multi-Purpose Module (MPM). All other electrical functions are working correctly, but this issue is affecting both safety and functionality.