Check the wire by the battery which connects to the solenoid. It sounds like you have power to the relay in the passenger side as you hear the clicking but it's common for the wire (connector) by the battery to corrode. Worth a look? Sometimes reconnecting it makes it work (as the corrosion moves):
See this post: http://www.f150forum.com/f4/starting...9/#post2139219
Otherwise I'd start checking voltage at the starter with a voltmeter. Securlok light isn't flashing like mad on the dash either right when you go to start? - Sometimes remote starters can mess with this if it wasn't installed properly.