So I have a 2003 chevy 1500 with about 293000 miles on it. I have been having voltages drops while driving. The voltage will drop only in the cab to almost 9 volts at times. The abs light l, parking brake light and sometimes the airbag and security light will come on too. This happens when the hvac fan speed is above 1 sometime it even happens on speed one also. It also happens if the music is turned up or if any other accessories are on in the cab. The voltage is normal everywhere else on the truck the only voltage drop is in the cab. I located all of the in cab grounds and cleaned them. I have tried swaping the dash cluster, the hvac module and it has a new transfer case control module. I have also taken apart and checked all the connections on the abs module. It also have a new fan restor. I've tried unplugging molutiply different accessories like the fan motor etc and nothing fixed it. My mechanic friend hooked up his fancy snap on scanner and determined it was not the ecu. I have also tryed putting different alternators on it and nothing worked. When it started I had no after market accessories in the cab. I can't seem to find where the voltage drop is coming from. If anyone has ran into this let me know

 

Welcome to the forum. Moving to the Truck section of the forum where you'll get more views.