The top one should be coming from the trans, and the bottom should be going back.
FYI those lines are actually going to a pretty large transmission cooler. Take that plastic piece off the top of your radiator and look down in the space between the radiator and A/C condensor. You'll see the trans cooler at the bottom.
You can still install an additional one. Just remove the input line from the original cooler and make that the input on your new one...then run the outlet line from the new one to the inlet on the old one. Should be a bit better than just 1 cooler.
