Two steps remain: wiring the CPL to function, and placing it in the yard.  This section is about wiring it to function.

A little about relays

I am fortunate to have a friend, Abe, in New Cumberland, PA, who has amassed an incredible assortment of signal...um... parephenalia...over the 46 years he's worked for various railroads - Pennsy, Conrail, and now a shortline in Pennsylvania. He's provided me with five relays:

three US&S DN-11
one US&S DN-22
and one GRS Type K

The relay ID panel pictured above is from my US&S DN-22; it shows, among other things, the manufacturer's name, the relay type, the coil resistance in ohms, and a diagram of the contact layout, with the diagram drawn with the relay contacts as viewed from the front of the relay.  Also visible in this photo is the inspection tag from the manufacturer, showing that the relay was made on July 17, 1942. The photo above shows the binding posts of a US&S DN-11 relay, labeled as shown in the diagram on the ID label.  One odd thing about relays is that, for some inexplicable reason, the binding posts toward the front of the relay are called the back posts and the posts toward the rear of the relay are called the front posts.

Below is a patent drawing, which happens to show a DN-11-type relay. Note the way the binding posts are connected to the relay contacts.  The wire connecting the "heel" post and the heel contact is called the "heel ribbon"; also note that the terms front and back have absolutely no relation to the position of the contacts, which are up and down.

Note that the armature - shown in red - is up, indicating that he coil is energized; in this case, the "front" contact is energized; when the coil is de-energized the armature will drop away from the bottom of the coil and then the "back" contact will be energized.  This concept is more easily demonstrated in the following drawing, also from a patent, showing the two positions of the armature; the red indicates the position of the armature when the coil is de-energized and the armature is "dropped out".