I know enough about electricity to safely swap out light switches, but an electrician I am not.

I'm using a high-quality controller to make my vintage Crouse Hinds 4-way traffic signal operate as it did in the field, with timed R-Y-G phases on alternate sides. For argument sake though, let's operate under the assumption that it's a single traffic light controlling only one approach.

The controller is designed to produce a three-phase, three indication R-Y-G cycle like we're all accustomed to. I'm trying to rig the connections so that it mimics an old-fashioned three-phase, two indication R-G signal, wherein R and G illuminated simultaneously equals yellow. Furthermore, I have a vintage round WALK lens in the green position, which should be illuminated only during the G phase. I have spliced and diced these connections every which way I can, and what I've learned is that electricity behaves a lot like water: it flows in every available direction.

When the green line fires it illuminates the green and yellow lights, as desired. However, in addition to travelling up to the yellow fixture, the current also travels down the other wire in the splice toward the red terminal connection, and up to the red bulb. (See the "What's actually happening" illustration, below.) So, no matter which line fires (G, Y, or R), in the end all three lights are always illuminated because there's an "up-down" connection to all of them through splices.

What I need is a wire connector that also restricts the flow of current to the destination wire, which is also the "root" of the splice, which is the hot wire to the light bulb. According to the following description, diodes appear to fit the bill: "a semiconductor device with two terminals, typically allowing the flow of current in one direction only." What I've read so far, however, indicates they are used primarily for computer peripherals and the transfer of data, not electricity.

QUESTION: is there some type of inline wire diode/connector I could use to restrict the flow of electricity as illustrated in the "What I want to happen" illustration below?