Help - what is this electrical box on rear of 2007 frame?

Could someone please tell me what this is? I pulled the bed off to fix some rot and while the bed is off, I thought I'd knock off the loose rust and paint the frame. There is what looks like an electrical junction box on the drivers side, mounted right on the frame that's badly deteriorated. I'd like to replace it, but I don't know what it is and can't seem to find anything helpful to identify the part. Thank you in advance.

 

I believe it is the controller for the fuel pump.

 

That's it. Thank you very much.