no sound,new stereo ford van

I am instaling a new srereo on a 94 Ford Econoline van. I used the proper harness (I think), they all plugged in. It appears to be the premium sound system. The stereo powers up but nothing comes from the speakers. I put an old speaker to the new stereo, and it worked. I put the old radio back in and the speakers worked fine. Whats up with this?

you must have the wrong blue wire hooked up. hook up the blue/white wire to the blue wire on the ford plug side.

Thanks, I'll give that a try and let you know.