I was poking around under the driver's seat of my 2006 E350SD extended cargo van, and discovered this attached to the floor (see photo):
Excuse my ignorance, but what is it?

 

I believe that's the RSC module for your year.

 

Close. It's the RCM. Restraint control module. Interacts with the airbag and the seat belt pretensioners. I had a flashing airbag light and had to replace one of these. I thought I was brilliant in diagnosing the problem until I replaced the part and it still was flashing. Had to go to the dealer to have them program the new one for about as much as I would have paid to have them do the whole job.

Where is the airbag module located in a 2006 Ford E250 Van

 

Learn something new every day----thanks Del!

My '03 E250 also has the pre-tensioners but no RCM installed or present as shown---both under seat areas completely open. I'm assuming SRS deployment is triggered or controlled either by the PCM or another module installed out of my sight.