67-72 Chevy Truck fuel gauge diagnostics 101

[CarpBlazer]

Ok, so I figured out my electrical gremlin causing stuck fuel gauge below empty. I was having issues with all dash lights (turn signals solid, high beam indicator lit, everything that could light up on dash)to go on when ignition on and as I said above, fuel gauge was stuck below zero.
After checking the whole harness, replacing circuit board (only to fry the ground connection again) and hours of scratching my head..I realized the factory tach hot wire was running from fuse box ‘ignition unfused’ port to the upper center post on the tach. Problem is, that upper post is the ground post..Face palm...I attached it to ground and boom, everything works.
Fuel gauge is now working perfectly. I’m now on a mission to find correct wiring for factory tach.
This thread really helped me tackle all this and get it solved, Thanks!
Ben