Electrical

My ram has electrical issues...
My radio is not getting enough voltage to run the
radio. My key lock and unlock button only work
while the truck is already on. My headlights will
sometimes come on while the truck is just recently
turned off. My dome lights do not turn on while
pressing the on button they only come on when the
truck is running and the door is open. All electrical
problems that started happening around the same
time. The dealership repair shop is saying my driver
door is sagging and pulling on my wiring harness
across and disconnecting and messing up the
electrical. The door hinges are now fixed and
electric is not okay at all. What could cause the low
voltage around my truck? I just had a new radio
installed and they bypassed the old wiring harness
to give the radio enough power. But my back
speakers are not working. I need serious help.