These signals are rigged to run using a common anode (the top wire in your photo with one resistor for the whole group). The color leads are the cathodes off the LEDs. Anodes go to positive, cathodes to negative.
How do you want your signals to operate? There's a lot of options when it comes to signaling. The ITAD is generally used to detect a train at a particular location. Will your signal show aspects other than STOP (red) and CLEAR (green)? Do you want yellow to mean something? Will you have your line organized into separate blocks?
Certainly the ITAD will produce a signal of some kind that will indicate that a train is present. But what do you intend to do with that information?
EDIT:
What I mean is, the ITAD will produce an "electrical" signal.
Your MTH cantilever bridge probably shows yellow for some short period of time after the train clears the ITAD. That's some sort of timing mechanism built into the signals; it's not from the ITAD. Didn't I read that there were tiny 555 timers built into the signal heads?
