[Perko]

Alan,
You didn't say what year that truck is, but some of the newer units control the fan through the bulkhead module and or the engine module. Either could give you trouble. Start by checking and cleaning every ground connection you can find, engine, frame, batteries, under dash, firewall, etc. Freightliners are very picky about their electrical grounds. Most good Freightliner shops can fix you up without picking your pocket to badly.
Perko