I tried one thing which is very interesting. I connected my hobby signal 74391 to the terminal tab of the M84, the red and green lights worked fine when I clicked on the icon from my CS2 for the M84, when I look at the plug (connect to the M84 tab) of the 74391, there are 3 wires, blue/red/black, and only the blue and black are connected to the signal itself, I surprise where is the ground (or return) of the signal since the blue and black are to power the RED and GREEN light and there is no extra return wire (the middle RED wire is used to connect to the 'stop track section' and sure not for return)?

I also connected the red wire from the plug of the 74391 to the 'stop track section', even I turned the light to green, but the 'stop track section' still had no power supplied. I needed to use an additional wire to connect from a 'powered track section' to the middle screw terminal of the M84 where I plugged the 74391 signal to the tab underneath it (i.e. the same output on the M84). I want to ask how the M84 is wired internally such that the middle screw and the middle pin at the tab for the same output can provide power to the signal light but does not provide power to the stop track section?

I also connect my street lights to another output of my M84, and I need to connect the power supply (from a transformer) to the middle screw in order to power the street lights, this means the middle screw is the only power supply for the red and green terminals, so I wonder how the 'stop track section' works for the above signal connection? How come the middle screw provides power to the RED/GREEN light but not provide power to the 'stop track section'?

Hi!
It only takes two wires to have full control over two anti-parallel LEDs.