Tranny fluid flow direction?

I am adding an external transmission fluid cooler. The instructions tell that the new radiator should be mounted in 'series' and 'downstream' from the main radiator's resevoir. All that being said...which of the tranny fluid lines is out to radiator...the one on the pass side or drivers side. The instructions say to disconnect both, turn the ignition key (make sure engine can not start) and monitor the flow. Just wondering if anyone knows off the top of his or her head.

Follow links to Joe Black's website -he has this info there under the "transmission fluid change" section.

Here ya go: http://www.antiquecaterpillar.org/vx...l/4L30E_01.asp