Anyone know where the other end of this wire is suppose to attach to? Its under the rear back passenger side wheel. Right under the bumper, see pics. Circled in red. It seems to be a negative ground wire, but to where?

 

i dont know about the wire; but is that a crack in your frame rail?

 

Yep, that frame is rusty. Looks like mine before I had it welded. Wouldnt pass inspection in Vermont. Funny, I saw that same wire when inspecting my frame rail rust and wondered the same thing as the OP.

 

that's the wire to the anti-corrosion system, no wonder your frame wroughted

 

Yup thats a crack, but for $450 for the whole truck and $25 to fix it (new used coils)i'm not complaining. I'm actually getting the frame rails welded and also the hanging wire goes to the gas filler tube, safety ground or something.

 

Flux capacitor......

 

Backup sensor plug? I know there were a few D2s fitted with reverse sensors, so I'd assume all of them were wired for them same as the heated seats.