After a deluge of 3 inches of rain I could not start my 94 Disco the next morning. I can hear a click which appears to be coming from the right front footwell which was soaked for some reason, or possibly the right front of the engine compartmentr. Other than that, not a sound or movement. Battery fully charged.

Dried everything out for a couple of days (heaters, fan) to no avail. Any suggestions would be appreciated.

 

Sounds like you have a near dead battery causing the starter solonoid to click when you try to start it. May want to see if you can jump start the truck off of another cars battery.
Mike