1994 silverado AM radio

I had a 93 Blazer with the same problem..S-10, but I think you might have the same type of configuration. It was my antenna, and where it comes into the engine compartment. About 1 1/2 feet were the antenna comes in under the fender, there is a in-line coax connector. mine was almost open , the connection was bad. I couldn't find another connector, like it, so I just cut the connector out and spliced the coax, neatly, soldered it and the radio AM static completely disappeared!! I pulled in stations from everywhere. The FM was greatly improved also! FM operates a little diferently, so that is why your FM still works ok. Just I few hints to maybe help you out. Andy