Having just installed a trans cooler myself last week, On a '02 liberty with a 3.7. I can tell you the size of the tubing 3/8 O.D. You can buy trans cooler hose at the parts store just for trans cooler lines in this size, will easily slide over tubing on raditior and on the cooler itself.(it's cheap) The trans cooler line you want to use is the bottom one out of the raditior, that should go to the new cooler (top fitting if mounting horzonialy) and then take the bottom fitting from new cooler and run some hose and couple it back into the bottom hose the stock cooler was connected to. So, what I did was, use the stock cooler, and then run the slightly cooled trans fluid through the air cooled trans cooler to get even more cooling of the fluid. this is probably the best method to plumb one of these up. After you get this done, check your trans fluid level, I had to add about 1 1/2 pints of fluid to get it up to proper lever on the dipstick, I guess the cooler adds a little fluid capacity to the trans.