Most Toyota and Lexus car stereos with Navigation feature or XM radio have the External CD changer port  already occupied by navigation plug.

In such case, the Toyota Y cable should be used in order to make GTA Car Kit and Navigation both work at the same time.

For installation – disconnect the Male navigation plug from the stereo, and in it's place connect the male plug on the Toyota Y cable. Then connect the navigation and GTA Car Kits male plugs in to the female connectors of Toyota Y cable to complete the installation.