Those black cubes are relays. You can feel them work when they get energized. If you now have a diagram of the fuse panels in the owner's manual you are making good progress. It is important to know how to locate a relay if necessary on the diagram in the owners manual. Also, in the fuse and relay section of the manual there will be a description of what circuit each fuse protects and what relay controls what operation.
Let us know if you have a good understanding of how to locate a possible defective fuse . Once you know your way around the electrical panels you can move on to isolating a drain or possible short circuit.

 

Ford E350 triton V8, 2003
Do you by chance know where I can see that electrical diagram online. I don't have the owners manual.

 

Go to, www.fleetford.com. Go to owner's manuals enter the info for your vehicle.