Long time reader, first time poster. Bed rusted through and was wobbly. It was being held on with one bolt. Front two were rusted through and back two nearest tailgate were gone as well as cross member if there was one. I would like to know what the part is over the rear axle. Is it important and what does/did it do? i have it hanging on with a wire and it is not plugged in. Tire carrier rusted off a long while ago. 2001 extended 4x4 4.0L. 408,700 glorious miles. 2 starters, 5 front and rear brake jobs, 16 tires. Thanks for the read and help!!

 

That's all your rear EVAP system hardware.
It's hard to tell how it used to be connected, there should be a line from it going to your fuel tank.
Ford very often changed these systems, so I can't say for sure, there should be a sticker diagram of its layout just above the rad in the engine bay.

Having it disconnected will throw up a CEL code, more of an annoyance though, the truck will run fine with it disconnected.

EDIT: I can see where the line from the fuel tank plugs into the carbon canister now.
Having that line off like that allows evaporation of fuel directly into the atmosphere, not so much a big deal as far as that's concerned, but you will lose some fuel in that respect.

 

and I thought my truck was bad. looks like you need a frame from the junkyard, all your rear cross members are gone

 

here's what it should kinda look like, this is my 99