Wire 1982 XJ650 Maxim

I recently picked up a 1982 Yamaha XJ650 Maxim as a super cheap project bike. So far, I’ve drained the old fuel, dropped in a new battery, and cleaned the filter. Everything else mechanically looked pretty solid until I opened up the headlight bucket and found a total mess.
I do have a key that turns in the ignition, but right now I'm getting absolutely zero power to anything.
Inside the bucket, I've got a bunch of disconnected wires hanging loose. Specifically, I'm staring at a mix of loose lines including Blue; red, green-yellow line hanging wires spilling out of the main harness sleeve. Also black female wires coming from speedometer and tachometer.
I tried downloading the service manual and wiring diagram, but honestly, looking at that schematic is just making me even more confused at this point.
Can anyone help me figure out what these specific connectors and wire bundles are supposed to plug into, or where a total loss of power up in the bucket usually stems from? Here are a few pictures of what I'm dealing with. Any guidance would be a huge!

 

Blue wire with a female bullet terminal: an extra hot (12V) wire, not used on North American models..........in the rest of the world (particularly the UK), bikes were required to have a "parking light" for use at night when the bike was parked on the street, and that 12V lead was for a small (flashlight-sized) 3-watt bulb that fit into the bottom of the headlight itself.

Red wire with a female bullet terminal: an extra hot (12v) wire, not used on North American models (but nice to have when adding accessories).

Green with yellow tracer stripe: goes to front brake light switch harness....should be a matching set of bullet connectors with a green/yellow-tracer wire and a medium-brown wire. The green/yellow wire and the medium brown wire are the "in and out" wires for the front brake light switch.

Dual black wires with dual female bullet terminals: ground wires for the left and right side turn signal light harnesses.

Total loss of power: either the battery is dead or not hooked up properly, or the main fuse in the fusebox is blown (or, if still equipped with the original flat, black plastic fusebox with glass-tube fuses, then the metal "clips" that grab and hold the main fuse (20A) have fractured and are no longer passing power to the rest of the harness. If not either of those problems, then the main fuse power output goes to the KEY SWITCH, and if there is a problem with it (internally; or, it's not hooked up) then that would be the next place to explore).

NOTE: it's always a good idea on these older models to replace the stock fusebox with a more modern ATO/ATC ("blade") style fuses and fusebox, as the original fusebox is a problem waiting to happen........

 

Omg thank you!!

 

thanks again for the detailed breakdown—that helped clear up a ton of confusion.
I snapped a few photos of my actual setup to check the power and fuse setup you mentioned. Does everything look wired and installed correctly here, or do you spot anything out of place