Also double check your grounds starting from the battery working your way to the body grounds. When grounding is not present, the electrical supply will "look" for a path and does not have a way to flow. As soon as something interupts what little current that is using feedback from lack of ground, it robs what little amperage being used to operate that system and falls below what is required to run it. It seems too coincidental that the majority of the system started showing these signs of no power all of a sudden. After you check every possible ground solution and it still has fits, then it's time to do good old detective work.