I have a 1993 E-150.L.A west.conversion van. I'm try to hook up a after market stereo I'm getting power to the deck no sound.there are a bunch of plugs under the dashboard.there is a stereo behind the driver's seat and headphone jacks I've hooked up stereos before but this is got me stumped

Kind of hard to diagnose with out more details and possibly some pictures to help. Could be a million reasons for no sound, but sounds to me like the previous owner got a bit carried away hooking up all sorts of nonsense if you have a stereo in the dash and behind the driver seat. Could be opening up a big can of worms.