Re: Going up the mast on a trailerable sailboat?
You can take down the mast, and slide it back far enough to test electrical stuff before you raise it again. Just support it with a temporary crutch, and make sure it doesn't see-saw.
My wife as been up the mast of our Tanzer 22 in a bosuns chair. Looking at the forces generated in sailing compared to body weight, we thought it to be reasonably safe, and used the main halyard. Might have employed a backup, but I can't remember.