Service 4wd question

[WRLIVE]

My 'Service 4wd' light on the dash is illuminated almost everytime I go to drive the truck. I checked the condition of the wiring and plugs on the transfercase and everything looks good. I replaced the motor on the transfercase which did not fix the problem. The truck still goes into 4wd thank God but I am sick of looking at the dash light. I took it in for an hour of diagnostic and they 'think' it is the transfercase control module. They will be happy to swap it out for me to the tune of $600. I know the part is $250 and I know where it is under the dash but I hate to waste the money if that's not the problem. Thoughts? Could it be the switch? Would that cause the light? Thanks for the help,