I can't tell you how many are too many, but as a young child I used to run ~7 wagons per train, all ran at top speed, never had a problem other than collisions (some head on) and trains flying off the tracks, that was the biggest fun.

To turn the signal OFF and ON you need the following:
X2 contact tracks
X2 thin small cardboard sleeves.

When you look at the signal's wires there are :
X1 Yellow = Power
X1 Red = Cuts track power to isolated section.
X1 Green = reinstate track power to isolated section.
X2 (Usually) Red with shiny metal connectors at each end.

when you lay your tracks you insert X1 cardboard sleeve in front and after the signal (The contact tracks you can add anywhere you want and run wires, depends on what you want to achieve.) This creates an isolated section of track. Inside this section you insert (on the contact tangs of the tracks) X1 red wire with the metal connectors, the other wire with the metal connector you insert outside of the insulated section, this way you can power the isolated section when there is a need.

Assume that you have X1 stationery train by the signal and you want another train to realises it and send it on its way, you also want that the train that have just left will turn the signal to RED so that the incoming train will stop.
To achieve this you need to connect the GREEN wire to the contact track that is positioned before the signal and the isolated section, this will turn the light to GREEN and the signal's solenoid will allow power into the isolated section. The train leaves the signal and then passes over the other contact track. In turn, this sends a pulse to the signal's solenoid that moves into an OPEN position and cuts the power to the isolated section. the incoming train stops.

I hope that this helps.

Ben

Maybe I do not understand the question, but once the signal changes to red, power to the section between track power insulators (paper pieces around red signal wires; see instructions) is off. The train won't move until you change the signal to on with a control box, and power to the track segment is returned. The contact track is an interrupt of one side of ground that activates side plugs when a metal axle connects the other outside (continuous) rail of the contact track. I have used this, for example, for lights when a train goes by. This is analog operation. In digital running, these tracks are used for occupancy feedback, telling the control station to do things (like setting signals).

Depends on the speed of the train also. If it stops over the block, then could burn out the solenoid. Feedback momentary contact is best.

thanks i do have one rail with 2 solenoids i have been putting of switching track as i hear they are less reliable