Three and four way with X-10 is not easy. The original setup used a master switch that had four wires and 2 switches that had 3 wires (not including any grounding), is this right in your case? If so, you will need to install the master switch where the switch that had four wires was. This is the master location and is where the slave switches will transmit. The slaves will require a hot and a ground. The wires that feed the slaves are located at the master. The wires are easily figured out using a meter. The way the original system worked is like this: One switch would feed a neg. and the other a pos. or vice versa. This would turn the light on having both needed poles. If the switch was changed then you had two of the same poles, there for no light. The master switch would allow either poles depending on the position (why it has 4 wires). It kind of works like a big loop with each switch having a say so in the chain. Anyway, Both slaves will hook up to a Positive and Neg. You will need to hook 2 wires in the master location to a hot and negative to send to the slaves. Then the wires that are left can be used to send the trigger to the master switch. It’s not easy to describe over a letter since so many things may be different. My suggestion is to hire a professional to install the 4 way for you. Also, trial and error works well. You will probably get a nice light show and be performing a few breaker tests but you will sooner or later figure it out.
