The headlight switches in these trucks are known to be a problem.
The H/L's draw their power through the switch creating a heat issue within the switch itself.
Hot to the point of burning wires & internally cooking the switch, causing large clouds of smoke to emit from the dash.
Some trucks have been burnt to the ground because of this power-drawn-through-the-switch wiring design.
Once that switch is cooked, nothing lighting-wise is going to operate properly.
Rewiring the H/L's with relays alleviates the heat within the switch, along with providing higher voltage to the lights resulting in them actually burning brighter, albeit with a slightly shorter bulb life.
Gotta give a little to take a little.
Brighter lights, though! These trucks need all the help they can get in that area.
Just another thing to check, because by what you describe, there's more than one issue here.
Start simple. A volt/ohm meter, a wiring diagram & some patience.
Check & clean all grounds. These trucks do strange-weird things when those aren't up to par.
Inspect those cables too. Is that green corrosion just within the first couple of inches or is it running the whole length?
Originals cables? Ugh. They're old. Upgrade! Do the big 3.
Make sure the basics are good before moving on to any individual issues. With these trucks, sometimes those most basic of basics can create seemingly unconnected problems in other areas.
I hate electrical gremlins!