pioneer 1900 deck on 91 ford e350

I am having a devil of a time installing this deck into my E350 chassis RV.  I paid for a Scoche (sp?) wire harness which did not have the wires set up correctly.  I used the wire guide noted on the site, however I still can't get any sound.  The ground switched 12v and constant 12v are hooked up correctly.  I believe I followed the wire schematics to a T, but no sound.  The only thing I can figure is the OE deck is @ 2 ohm and my deck is between 4 to 8 (noted on the box).  Is there anyone who can shed some light on this for me.  I easily have 3+ hours on this deck which should have only taken half an hour.

Any help will be appreciated.

It has 4 speakers, two door and two in the rear.  There is a center speaker grill opening on the dash, however there is no speaker there, but what looks to be an amp (it has heat sinks around the perimeter).  The chassis doesn't list this stereo as a premium system, which would have the amp, however it has some of the hardware the premium systems has.

I was told by a friend that on the OE system, the neg to the speaker (ground) acts as a common ground and as such, will sometimes blow out the speaker output of a traditional DIN unit (damn Fords) since the front and rear speakers outputs ground to the same speaker as opposed to each speaker, if that makes any sense.

I have pretty much given up and I'm taking it to a stereo shop to have them install a inexpensive CD player with whatever harness or module is required.  If you happen to know what I will need, then maybe I can let them know I know what is needed to save myself from being duped.