It can be done. Back in the 90s I would photocopy the complete wiring diagram at the library, usually over multiple overlapping pages. Then at home I would tape the pages together to make a large sheet. This was before photoshop and internet. Now you can print out multiple pages to get a big sheet.
Use a pack of colored highliter markers to put in your colors. Use the red to start from the battery to mark all wires that are 12 volt hot. This includes wires to the alternator, fuse panel, light switch and ignition switch. Next take the orange marker and color all the wires that are only hot when the ignition switch is in “run”position. Use blue to mark all lighting wires when the light switch is on.
Use a yellow marker to color all the individual devices, switches, relays, etc. You get a quicker overall view when the devices are colored. Use a fine black pen to label the actual colors of each wire, following the color abbreviations at each wire.
You can break down the task by filling in each bit you are sure of. Then figure out the tough wires and label them. The diagram usually shows the firewall connector as 2 halves, drawn as mirror image or rotated by 90 degrees. Mark a few terminals on the firewall connector so you can quickly see which goes to which.
Compare your actual fuse panel to the best diagram you can find. It can be done!