Each radiator has two hoses, one in and one out. When you install the new hoses with the extra smaller hose for the center radiator you have to make sure you install them in the correct direction. Each side gets one new hose. You should be able to figure this part from the different DIY instructions available online.
The issue with adding the center radiator to a Base model is that the coolant system hoses are smaller than the S.
Some background:
The radiator connects to a rubber hose (the same ones you swap to add the center radiator), which connects to a metal pipe that runs through the wheel well, that connects to another rubber hose, then goes farther back into the cooling system.
The radiator connection is the same size for the base and S, however the other end of that hose is a different size between the S and the Base. So you need to modify the system somewhere.
Option 1: Find a welder to enlarge the metal hose on one end (this is what I did)
Option 2: Modify one of the rubber hoses, like the Pelican article describes
-The issue here is that with the T-fitting for the center radiator, there is not enough room to splice two hose sizes together on the front hose. So the Pelican article replaces the metal tube with the larger S one, and modifies the rubber hose behind that to be compatible with the rest of the base coolant system. The Pelican article does not explain this clearly at all, and requires purchasing two S pipes, and the two rear rubber hoses.
Best of luck!
This thread may help:
http://986forum.com/forums/general-discussions/58129-center-radiator-retrofit-base-s-hoses-thoughts-best-solution.html