Writing new wiring diagrams - computer program?

[Loneranger]

I have added several electrical items to the boat over the last year. I plan on updating the factory wiring diagrams to indicate the new additions. Some items will be easy to do by hand but the stereo is a bit more complex so I was going to replace the factory page entirely with a new one. Is there a simple free program that is useful to produce wiring diagrams?

Also any suggestions on a label maker for wires? I tried the label maker at the office but could not make them stay. Currently all the wires are labeled with a small sharpie.

John