this found on the forum. " This harness will allow you to plug in the OEM JBL harness into the little black box. The device utilizes the stock JBL system with the new HU. Axxess TYTO-01 (tyto01) Wiring Harness for Select 2003-2008 Next, you will need this harness. Metra 71-1761 (met-711761) Reverse Wiring Harness for Select 1987 This harness will plug into the back of the Scion HU. Basically, all you have to do after that is match and crimp wires."