Troubles with adding AUX input to factory Delco

Good evening all, I am doing a restoration on a 1983 Trans Am which still has its factory stereo. What seems like a simple procedure is kicking me in the rear right now. The plan was to add a Radio Shack 274-246 3.5mm jack between the L/R input wires that go to the amp... The tuner and cassette still work great after wiring in the jack... It's when I plug in a external source to the jack that I have very quiet garbled sound. If I remove the ground cable on Pin 1 from the equation, I then have left channel sound to both L/R speakers and right channel sound to both L/R speakers... When a reapply the ground cable I have L channel sound to the left speaker and R channel sound to the right speaker, but very muffled and garbled... Does anyone have an idea or tips. I have tried many things to no avail. Any help would be appreciated.... Here is a link that explains what I have done so far... Part 1 http://eurosportvr.com/misc/ipod%20input/index.htm Part 2 http://eurosportvr.com/misc/ipod%20input/Doc1.htm

http://www.newegg.com/Product/Product.aspx?Item=9SIA2KM2TS0210&nm_mc=KNC-GoogleMKP-PC&cm_mmc=KNC-GoogleMKP-PC-_-pla-_-Cell+Phone+-+Cables-_-9SIA2KM2TS0210&gclid=CKuyhJvCwcwCFRSPfgoda30JLg&gclsrc=aw.ds have installed plenty of these into peoples cars who just want a aux cord and they work amazing.