Which tube on the bottom on the radiator (factory cooler) is the tranny oil RETURN tube?

I looked at my tranny and I see 2 tubes that connect to the radiator, one that is towards the passenger side and the other tube is towards the driver side? so which tube is the one that the oil is coming out of the factory oil cooler and RETURNing back to the tranny?

Instruction says you have to connect it in series w/ your stock oil cooler inside your radiator, so the tranny oil has to flow through the factory cooler then through new tranny cooler.

Instructions shows you how to find out the oil flow direction but it involves disconnecting your distributor coil and disconnecting one of the two tubes and placing the tubes in an oil pan cranking the engine to see where the oil flows out... dont want to bother with all that mess.