Making wiring harness

Bought a length of asphalt covered loom from Brillman. My question is how is the best way to break wires out of the main loom at connection points (regulator, coil, generator, etc)? Do you make a hole in the loom at each connection point and thread the exiting wires thru, or do you cut the loom into pieces, pull the exiting wires to the side, and seal the loom back together where you cut it? If so, how do you seal up the loom?

I"ve noticed that commercially made harnesses neck down to smaller diameter loom as there are fewer wires left. Can you use heat shrink tubing to join the different loom diameters together? I"m sure I could use electrical tape, but I"d like to get it to look like the commercial ones if possible.

Any suggestions and help would be appreciated.

Take the original loom and lay it flat on the floor.
Place the new "Tube" and place it next to the original.
Use a straightened piece of #14 galvanized wire long enough to go end to end, to pull wires into the loom. Sharpen the end to allow penetrate the loom in the same olcations as original.
Start with the shortest, and end with the longest.
leave 2" more wire than needed on each end of the new wires. Use heat shring tubing to attach new wires to the pull wire. Also use it to seal terminal ends to the new wires.
Just my method,
JimN