Someone pointed out that my tail light wasn't working. I did a little digging on Thumper Talk and found this thread.
Since my battery is dead, I took it out. Without a working battery (or without one at all, in my case), the tail light doesn't work on the 250X. Whew! Now I don't have to worry about tracking down an electrical problem.
A commenter suggested this link for fixing this issue: http://www.crfsonly.com/forum/viewtopic.php?t=34768&sid=1940189b6e0c5b9a7f41f1bca10c465e