97 ford f150 xlt radio issue

My customer has a 1997 Ford F150 XLT with only a stock casette d/din radio and when i pulled it out,it has one gray 8 pin rectangular harness(has power/ground) and the other harness is a black 16 pin square harness with 8 pins in a row each.There is antennae plug directly behind radio so it does not have a separate tuner box, speakers dont have separate tweeters and does not say premium system either.Confused how this would have an amp. Would a metra 70-5603 harness work as amp integration and if i have to bypass the stock amp,where is it located. Thanks

Maybe its a late 1997?  will a 70-1771 work on the 16 pin? you shouldnt need both factory plugs.  One might be for rear seat hookups.