The Fuses tend to acquire oxidation on where the "Pointy ends" contact the holders.(If you clean the holders use Bronze Wool,for smooth shiny contacts.)
The Fuses tend to develop "Microcracks" that are invisible to the naked eye.
"Looking At" the Fuses is asking to be fooled.

You are missing Ground(s),You've proved that.
Where ever you "Created" the new grounding point is NOT.
(If the lights or Turns are affecting the Alleged "Ground")

I'd pick up an inexpensive DMM (Multimeter) from Sears or Your Local Chinese
Communist Embassy (Harbor Freight) and FIND OUT What's Amiss.

The Wiring Diagrams,Electrical Trouble-shooting Manual and everything else you need is here:
http://w124-zone.com/downloads/MB%20CD/W124/Index/Groups/24ElectTrbleShting.htm

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'84 300SD sold
124.128