I have a RayPak boiler that currently has a W and R wire only. In wall i have a 5 connector thermostat cable so I have three extra wires I can connect to.
I'm a little unclear if it matters if i splice into the yellow line or the red line that I drew on the picture. Its much easier to access the yellow but I'm having trouble figuring out from this diagram where the R and W wires that go to the thermostat are, also I'm assuming that to get the power flowing correctly the C needs to come off one of these terminals and not the other. Is that correct?
Any guidance is appreciated. I'm attempting to install an Ecobee3 which mentions here that I can could pull a new 24v wire to install it: https://ecobee.zendesk.com/hc/en-us/articles/227874667
Perhaps a better question is which of the 24v lines is actually the common one in this diagram?