How do you know it's the circuit board ? What rear door ? Sound's to me like your best bet would be to take your vehicle to a qualified repair shop . Are your guessing or did you test ? Scan tool to check for diagnostic trouble code's ?
Have the vehicle checked for DTC'S - diagnostic trouble codes ! Do you know what electronic throttle control is ? The gas pedal assembly has electrical connector an sensors inside ,hooked to the PCM / ECM - engine computer . The engine computer uses these position sensors inputs to control the DC motor on the throttle body to open the throttle plate to control the speed . Plus there are position sensors inside the throttle body to input PCM/ECM to see if it's calculations are corect . Your best bet maybe to take it to a qualified repair shop . Drive by Wire Function and diagnostics by Wells
Reduced Engine Power Mode
When the PCM detects a condition with the TAC system, the PCM may enter a reduced engine power mode. Reduced engine power may cause one or more of the following conditions:
• Acceleration limiting--The control module will continue to use the accelerator pedal for throttle control; however, the vehicle acceleration is limited.
• Limited throttle mode--The control module will continue to use the accelerator pedal for throttle control; however, the maximum throttle opening is limited.
• Throttle default mode--The control module will turn off the throttle actuator motor and the throttle will return to the spring loaded default position.
• Forced idle mode--The control module will perform the following actions:
- Limit engine speed to idle by positioning throttle position, or by controlling fuel and spark if throttle is turned off.
- Ignore accelerator pedal input.
• Engine shutdown mode--The control module will disable fuel and de-energize the throttle actuator.
When the ignition is turned on do the console lights all go out?? If so it could be the positive wire that goes from the battery to the started. Could also be the relay, fuse, neutral switch (in neut and try).
After you get the truck started disconect you battery cable and see if the truck continuse to run. if it dies you are having a problem with the charging system. make sure dont have any interior lighs left on.
If your signals & brakes are on 2 different circuits, ( for example a red lens for stop & an Amber for turn.) then you'll need to buy a converter that goes between vehicle & trailer. They're not too expensive at any trailer or RV place. I think some of the autoparts stores stock them now too.