As I understand it, you will be powering the 153IR with 14V AC Accessory Power which would be hooked to the two left terminals (A=hot. U=common). Then set the center power selector switch to the ACC Power position.
If this is the first time you've messed with an Infrared Track Activation Device, I suggest you first set the Delay adjustment control to minimum, and the Sensitivity adjustment control to mid-range.
At these settings, you should be able to wave your hand or any light colored piece of paper several inches in front of the reddish sensor window and trigger the unit. If the room is quiet, you should be able to hear the internal relay "click" or "tick" turning on when you trigger it. Then, when you move your hand/object away, the relay will click again turning off. Or you can be ambitious, jump ahead, and hook up the flashers/speaker as shown above (blacks to ACC GND, reds to NO) in which case the flashers/speaker should activate/de-activate and you probably won't hear the relay click since the speaker will be clanging (hopefully!).
Once you confirm the unit is triggering and turning power on/off in, then you can mess with the Delay and Sensitivity controls to fine-tune how you want it to operate. If the reddish sensor window is next to a track, you should be able to adjust the sensitivity to detect virtually any passing engine/rolling stock. There are some oddball items with dark colored, matte-finish surfaces that may give finicky performance but few and far between. At maximum sensitivity you should also be able to detect lighter colored objects on a 2nd parallel track. The reason you wouldn't set it to maximum sensitivity might be because you have some light-colored scenery or object on the other side of the track causing a false reflection. Note that the 153IR is shooting a beam across the track and triggers when it gets a reflection.
