So I'm just a dumb guy trying to interpret schematics & other resources to suggest causes (no Rocket to look at)
And I look at schematic & see one thing; but looking at hardware I see something else;
not shown on schematic, there is a sub harness from the main instrument connector to the two individual connectors for each instrument
Interesting that there is different part number for the sub-harness that kicked in at serial 322157 which
might be with the break-out connector.
Odo Trip Resets
Tach does not sweep
If problems are on BOTH instruments. you have to look to common factor - that again points to the power source i.e. The Purple wire or perhaps the Ignition Power - Green/Red* or illum Power Red/Blue
It also suggests unlikely to be an instrument failure you could reasonably deduce?
*Note there are two Green/Red wires with completely different functions - just 'Brilliant' Triumph.
(that has been the same regarding those colour designations for ignition power and left turn on just about every Triumph in the Hinckley era)
Also inspect the two plugs into each individual instrument itself; also, there has to be splices somewhere on that sub-harness since there are common wires to each gauge.
One other interesting note is the reference in the update statement that says "poor connection
AND ELECTRICAL INTERFERENCE"