Decredenza, you're probably feeding a Line-Level source (ICS) into a Mic-Level port (recorder). It's overpowering the input circuit, so you get garble. What you need is a -40dB pad to bring the level down, or run it through a mixer or other attenuator. Then, you'll get clean audio via the cord.
John R81's solution is totally viable and people have been doing it this way for decades. Nothing wrong with that.
If you do want to stay the Corded route, a U/174 to 3.5mm with an attenuator will do it. Also, check your recorder to see if there's a Mic/Line Level switch. Many have one, and it will help greatly to change it to Line Level.
I feed ICS right into my helmet-mounted GoPro, and it sounds great. It goes in via the Mic Adapter, which can be set for Line-Level and works perfectly via a U/174 to 3.5mm.