Since I can't find a photo to confirm, can anyone tell me if the parking brake cable equalizer bar is supposed to be mounted to the frame? I can't imagine this part of the assembly is supposed to be hanging free like this…
Parking brake is not engaged in this photo

 

No it is not supposed to be mounted to the frame, but it is not supposed to dangle that low. Farther forward there is a frame mounted brake cable holder.

When was the last time you replaced the complete rear brakes?

 

Okay, the frame mounted cable holder is intact, as is the rearward one (where the left and right cables mount).
To be honest, I don't know when the rear brakes were completely redone (I purchased this only a month or two ago), but the pads look relatively new and the rotors have plenty of life left.
Doc, do you think it's as simple as an adjustment of the nut on the threaded rod? (That's where I was thinking of starting…)

 

You have more than a simple adjustment going on. I think your parking brake is either stuck (seized) or they are worn out?

Here is some reading for you.... good luck.
H3 Parking Brakes

 

Thanks for the link—should've known to search his PDFs!
My guess is worn out, since there is very little brake pressure, even when the brake pedal is pushed to the firewall… f@#k me, not what I needed now!

I appreciate your help Doc!