Sounds like a strange short somewhere. It could also be the alternator or the regulator. The heater fan runs only when the motor is turning by means of a relay that runs off the regulator to tell if the alternator is charging. Fuel pump runs the same way, and may be the source of your trouble starting. (Either running all the time and a leaky needle valve has the motor flooded with gas, or not running and not getting any gas)
I had a short in the wiring on one of my LUVs that puzzled me for a couple days. The main wire to the alternator from the battery had gotten hot sometime before I owned the truck and melted the insulation. It finally shorted to something else in the harness and I had a truck that would not shut off with the key. Motor running, turn off the key, motor still running. I finally tracked it down to a a short between the alternator wire to the bat and a wire to the switch for the backup lights. The backup lights were not on, but it was back feeding the ignition and coil from there so the key could do nothing to turn it off.
If you see any signs of burnt or melted wires, start peeling open the harness and tracing stuff. That main black wire to the alternator seems to be the most likely suspect since it is hot all the time and prone to getting cooked. I still think in my gut that the regulator is the real source, or a diode in the alt., but both are more expensive to replace. A lot of parts/battery shops will test them for free though, just be careful of them trying hard to sell you a new part. Take the parts off the truck, bring them in, and say "something just ain't right". Let them diagnose the parts only, not the rest of your symptoms.
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