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Voltage travels through the battery light bulb and down to the alternator. the alt grounds the wire to turn the light bulb on if their is a problem with the alt. your alt is defective. I have seen this on many fords. sometimes the only way to get it to turn off is to use a factory alt.
you changed the crankshaft bearing? hopefully it was Bearings. If you disassembled the engine to do this you should have replaced all the other bearing and checked for excessive wear in the engine. generally not a job for the do it yourselfer.
What size engine is in this truck? a couple of thoughts when is the last time the truck has had a tune-up? Is this truck carbureted, should be fuel injected.
I would start with the basics. confirm correct ignition timing, check for vacuum leaks, confirm good fuel pressure, make sure there is no egr flow at idle. some other things it could be are the map sensor, engine mechanical issue, weak pick up coil in distributor, or dirty/contaminated fuel injectorsYou can jump the relay just to see if the clutch does in fact work. you can do this with the engine off. These systems use a solid state relay if I remember correctly and they are prone to failure. The pins for the clutch should e the two big ones. Also you could just switch that relay out with another one like it in the box and see if it turns on then. If none of this works next step would be to check and see if you are getting battery voltage on the wire near the A/C compressor. If so also check for ground on the compressor itself. Grounds through contact with the block. If all that is good then most likely bad compressor
Yes the open loop thing is normal. It depends on the design of the fuel pump as to where the check valve is but as you stated and as I stated the likely hood of this being the cause is slim. Have you ever seen scan data when the no start happens to see if you do indeed have an rpm signal while the vehicle is acting up? Crank position sensors seem to be a common issue for these vehicles as well. An intermittent CKP is a more common issue in general.
Most vehicles use open loop when starting and only start using fuel trims once the engine stabilizes. I would be concerned with this. Possibly an issue with the EVAP purge valve sticking open. This is a normally closed valve that opens when energized to purge the charcoal canister of gasoline vapors. If stuck open it could cause the symptoms you are describing. Also maybe the but unlikely that either the fuel pump check valve is allowing the fuel in the line to drain back down and creating a hard start but that would not cause it to run rough at start up. you could check this by putting a fuel pressure gauge on and seeing if the fuel pressure drops rapidly after you shut the engine off.