Next question.... If I were, in the future, to tow a trailer that would then draw power through the trailer plug wire that I tapped off of, would this then send a potential 40 amp maximum charge (while towing the trailer) up and into the 5 amp fuse in place for the bed lights? I.E. would this then cause the 5 amp fuse to blow every time I tow?
No, there would be no problem. The voltage is 12 V everywhere. (14 when the alternator is running). The lamps will take nothing when turned off, maybe 1 A when turned on. Nothing that the trailer can do will change the voltage much, so it will have nearly no effect on the current the lamp takes.
Current has to flow around a circuit. When your trailer takes some current, current flows from the battery, along the 10 gauge wire, to the trailer socket, through whatever load in the trailer and then down the ground wire, back though the ground connection on the trailer socket, through the chassis and back up the battery negative lead.
No other wires have the trailer current flowing along them if the trailer is the only thing turned on.
In your truck, the starter motor probably takes 300 - 500 A. Your 40 A trailer supply is tiny compared to that, but it taps off the battery and the 0 gauge or bigger wire that can, and does, provide 300 - 500 A. Well that 40 A fuse (or any of the fifty or so fuses in the truck) don't blow just because you start the engine.
The only possible issue is that if the trailer shorted, that would blow the 40 A fuse that feeds it, so the truck bed lights would go out, until you removed the fault in the trailer and changed the fuse.
Separate circuits are used where you need to protect against faults in one circuit from blowing fuses that stop other circuits. Generally trailer circuits have fuses so that a faulty trailer can't affect the truck too much, but as it is only the truck bed lights, it wouldn't be dangerous if they turned off unexpectedly because of a faulty trailer.