How do I hook up another amp and sub to my 2012 f150 w/Sony hu
 

I've been trying to hook up a sub and amp to my truck for a while now got a harness from Amazon that hooked up to the back of my deck which added two sets of RCA's I tried hooking up an app is up to that but it just had distorted sound come out of the sub can anybody leave me in the right direction

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