Issue 1 and 4b "sounds like" what happens when the front lighting harness doesn't have the ground wire attached to a good ground. Wire could be broken, loose or not attached at all.
Issue 2 and 3 could be related. Poor connections at the harmonica connector or the printed circuit falling apart.
At least on F bodies... The tach has its own power wire that plugs in the back of the tach. So for it to work and other gauges not work is understandable.
Got to ask, Did this car come factory with ralley gauges or converted from lights to gauges? Wire pin-out in the harmonica connector is different between the two and can/will cause all sorts of problems.
Clay
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