Just an update - I removed the starter and tested it using jumper cables and it worked great. Then looked more closely at the battery cable and noticed a faint crack where it connects to the battery terminal. I think it conducted enough current to work the lights / horn / etc, but couldn't support the current draw of the starter. So bought a new cable for $12 and all is well. Thanks again for everyone's troubleshooting advice - I learned a lot and appreciate it.
Billy
