why radiator fans won't come on?

i have a 1997 plymouth grand voyager se 3.0 and my fans won't come on. i have straight wired the fans, and they came on. i checked terminals 85/86 for continuity and there was continuity in the relay. i sent power to 85/86 terminals onthe relay and checked for continuity on terminals 30/87 at the same time, and they all checked out fine. i checked the wiring for the fans and there were no knicks or disconnections. the fuse is fine also. the only thing i could not check is to see if the computer was calling for the fans to come on when the van reached the required temp. what else is there to do to fix or diagnose the problem. thanks