Reebok59
Member
As you may already know, the UQS system is a 9 channel 5.1 surround sound system. Where the UQA is a 6 channel system. The 4th plug on the amp (J4) is for the surround sound channel inputs to the amp. The inputs come from the Radio and the RSA (rear seat audio) Module. You need to reference the Light Duty C/K Truck Electrical diagrams for more information.
Hope this helps,
Scott
Hope this helps,
Scott