Somehow I didn't check to see if there was an install manual in the box. There wasn't. (It was used, but I have the manual from the unit I purchased new).

So they winged it. There are 3 flaws, 2 of which stemmed from this:
-the RCAs were plugged into the player instead of the sled. easy to fix
-they did install the 4 channel amp, but bridged the front and rear at the amp since they were confused. needs to be fixed, but not a huge deal

The other is more annoying
-the amp is bolted under the seat but seems to be too far back, so the rear passenger will probably kick the wires.

Nothing's ever simple, but at least it works correctly.