All the signals will show red when there is no activity on the line. When in surveyor to check if a signal is work properly you need to place a train (making sure it's green direction arrow is facing the signal) just before the signal. If the signal does not change then a few things need to be checked, make sure all switches are set for traffic, there are no tracks on dead ends that do not have the proper signal end barrier, make sure all track is connected, there are no other trains or cars on the line between signals. Hope this helps.
Rick