I have an old 20' racing sailboat where the outhaul is mostly missing. The wire is there at the end of the boom, but there's no rope coming out to cleat it. How can I run a new rope through the boom? Do I have to take it completely apart?
This will depend entirely on the type of boom and outhaul.
If you have a simple straight through outhaul:
If you have a boom with internal pulleys to increase your purchase then you will find this much more difficult: