Hmm.. I do recall saying something earlier about a silly mistake - never thought to check resistance. I forgot my basic electrical theory I guess. I was led down the wrong path after first connecting the power wire to a grounded sensor on the thermostat housing (tried to find the wire for the solenoid by checking continuity between the harness and the terminal - first ground wire I came across made the box beep, so I went with it. Oops.) and then becoming obsessed with short circuits afterwards.

Any idea as to what the backpressure solenoid might do? As in, what system (EGR, quick warm up, etc.) it is part of? Hopefully it's not essential to running the engine, as I have no controller for it at all.

Thanks for all the input, you guys really helped (as usual).