I just installed an older CD/Stereo reciever in my 2004 Chevy Express Van. The CD sounds great, but I am having troubles with stereo reception. If I disconnect the antenna from the receiver, FM sounds great, but I do not get AM. If I reconnect the stereo, I get a lot of static on FM, but AM sounds good most of the time. BUT... Whenever I go under bridges or near similar structures, I get this horrible undescribable static/feedback noise that makes me want to come out of my skin, this is really annoying because I take the freeway to work and have bridges/overpasses every 1000 feet. I have no idea what the problem really is. I used the antenna adaptor that I bought from Circuit City that allowed me to plug my car antenna into the receiver (they have different sized connectors), and used the $15, harness from them to plug my car harness into my receiver. I do however have to modify their harness slightly because the yellow wire was in the wrong place and it would not power on. I also noticed that I have lost all of my warning chimes (lights on etc.) and my radio will not power off when the car is off and the doors are opened like my factory radio did. I actually have to power off the radio each time, which is kind of annoying. Can anybody help me out. Thanks!
Most of your problems stem from you using the incorrect harness. The vehicle you have has a data bus system in it that is called class 2. In a class 2 vehicle the radio is on the data bus and is controlled by the BCM. That is why you only have a constant wire because the BCM turns the radio on digitally. Now by using the proper harness with a computer chip in it to replicate what the factory was doing would solve all your problems but the reception. As far as the reception goes understand one thing, nobody makes a better am radio than Delco. Most any old time installer or Delco tech will tell you this. So anything you do besides the factory radio will be of lesser quality than you had. Also, anytime you have break in the signal chain (antenna adapter) it will cause more resistance. AM relies heavily on a good ground. Also to make matters worse is that most aftermarket radio manufactuers do not concentrate too much R&D to AM. I have dealt with this quite often. So, in your situation do this. Get the proper harness, which I use a Metra piece (GMRC-02) and make sure the radio you are using is known for having good reception. I have used Pioneer and Alpine with good luck. Also, I don't know if they still do or not but Delco use to make the tuners for the Rockford Fosgate radios.