Sounds like you are making progress in the process of elimination. One thing you might want to try is the "Old rotating of the fuses in their holders" routine.
Often the fuses get corrosion at the ends where they make contact. The fuses with the aluminum links are very prone to this.
Ideally replace all the aluminum ones with copper ones. In the short-term check each fuse. At a minimum rotate each one.
This is another thing I would do to eliminate any fuse related items.
Some people spray a bit of WD40 on them or use it on a rag to clean the contacts and the fuse ends. WD40 does allow electrical conduction.
I do not believe the wiring harness issue was centered around the overall system, but only related to the engine harness.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)