I'd say to start with checking/cleaning grounds first.. There are a couple to go to first. there should be ground wires going from the core support down to the frame, check the engine to frame ground usually located on RH rear side of head to firewall. there a ground under the bed for the rear harness. (it's location might vary) There's also one up under the dash above the hood latch parking brake release. It's kind of a bear to see and get to, but you'll know it because it has I believe 6 prongs on it. Also, the bulkhead connector at the fire wall (on the engine side) is a good place for some headaches to start and end. Try taking it apart and checking for corrosion and make sure the pins are clean. That's where everything from the inside of the truck meets everything for the outside of the truck. I've seen those have corrosion and moisture in them and they can be a source for stray voltage and bad ground or power getting across pins and back feeding onto other circuits. Since you have a couple different issues going on, checking and cleaning the grounds and taking apart the bulkhead connector and inspecting and cleaning it will be good places to start. Just be careful on the bulkhead connector, there's a couple different connectors all tied into one. Also, I've had issues with headlights like you describe being right at the connector on the back of the headlight bulbs. They are often dry rotted and brittle so be careful taking them apart, but i'd look there first for the headlight stuff. sometimes a dab of antiseize will help with connection issues. just take it one step at a time and eliminate what you can.