when i put my loom in i first sat down wit a beer one eve and with pen and masking tape idented the end of each wire end.
then when i came to fit i pulled the cables in starting from the middle of the car dont worry about conecting anything up just route the wires where thay need to be and coil up the ends to length
then when your happy mount up fuse box and bits working from center to front and back
flexi split conduit is a god send when it comes to making a loom
well worth the few quid it cost