I noticed you mentioned the 15" model but tagged the 13 inch. Assuming that you have the 15 inch model, [guide|26370|here] is the disassembly guide, and you can stop when you get to step 38. [guide|27413|Here] is the trackpad replacement guide (meant for the 13 inch, but it still applies). You can order the part [http://www.ebay.com/itm/Macbook-Pro-15-Retina-A1398-Late-2013-Touchpad-Trackpad-Cable-821-1904-A-New-/181642695414?pt=LH_DefaultDomain_0&hash=item2a4abf92f6|here]. Before you purchase the part, check to make sure the trackpad ZIF cable is properly seated on the logic board and is not loose, since that could also be causing your problem. These cables are sensitive and can become dislodged.