I'm asking this question for a friend, so I hope I can answer any additional questions without him.

He has a '05 C1500 with the AM/FM/XM/CD/Tape head unit. He is trying to plug in one of those cassette deck adaptors to run an external audio source (he is plugging in a laptop to play dvd's) found at any Radio Shack or elect. store. The radio keeps spitting out the tape- won't play it. He tried it in a friend's Expedition, works fine, it worked fine in his previous truck ('02 C1500). A normal cassette works fine in his radio, but it will not let the cassette adaptor work. Any ideas why??

Make sure both wheels or "sprockets" (dummy tape spools) move freely. If it senses resistance, it will flip-flop back and forth. Another thing to check for is that the wire is positioned in a way that allows it to insert correctly. Before I changed mine out, I had slight trouble getting it to "play".

I know the sprockets turn, I did ask him that, but I do wonder about the wire thing. I can remember mine a long long time ago was figgity like that.

Update; he went and bought a new cassette adaptor, all is well.