fuse box power and transmission stabilizer bolt

Hi folks,
It's been a couple years since I've been on here as I don't keep the 'burb around anymore but like any good diesel truck it refuses to die and keeps showing back up in my life. And then I wrench on it a bit.

So question 1 is power: I've got all new lines and great voltage going from the batteries to the cab, but then between the firewall and the instruments the voltage goes to hell. I can't figure out how power gets from the primary engine wire into the fuse box, but I'm thinking it's the weak link. Any leads? or what to look for on the back of the fuse box?

Question 2: There is a rod that extends from the transfer case up to the engine block I believe. It only exists on the passenger side and is clearly for extra stabilization. The bolt to connect it to engine block is gone and it's just rattling. It's a big bolt, and without buying a ton of bolts at different sizes and thread pitches I can't figure out what goes in there. Anyone know?

Bonus question #3 to keep it diesel: has anyone ever installed a smaller turbo that spools up quicker than the Banks Sidewinder? After using it for 7 years I've found it's only good for top end power on big hills and not much else.