WOW! Thanks for all the good info. The checks that I did were only on the GPI connector on frame - short various wires and look for gear indicator or neutral light to show - nothing on dash lit up.
I hope you were actually shorting pins on the harness side of the connector and not the switch side of the connector.
The actual GPI was replaced when I did the spline lube. Haven't yet disassembled the dash to do the checks and tests you propose. Will do. Thanks for all the good leads. When I struggle through all of this, I'll report back my findings.
It's unlikely that the GPI board is defective. I've seen and heard of the LCD display going dark because that is a normal failure mode for LCDs.
In any case, there should always be some number between 1 and 5 indicating on the dash when power is applied and the TGPI switch is connected to the harness. If the display is blank, then that could mean the switch is open circuit in all positions either because the common Brown wire is disconnected or the pin for the Brown wire is not making with its counterpart in the harness side. In other words, all three inputs to the GPI on the dash are high, indicating a "7". But you said you changed the switch on the transmission for a new one so that can't be the cause.
The correct test is to disconnect the TGPI switch from the harness connector, apply power and use a short jumper wire to bridge any of the Yellow wires to the Brown wire on the harness side. Depending on which one you short, the dash will indicate either a "3" or a "5" or possibly a blank display. If you get nothing but a blank display no matter how you jumper Yellow wires to Brown, then there is a connection problem with the 24 pin connector at the instrument cluster.
I've never seen a K-bike instrument cluster without a clock but that's just my experience. If you have a clock module, it will be located just below the BMU indicator. It either works or doesn't work. If it's present but not working, power is not being supplied to it. Check the condition of the two power pins indicated by Inge above. You may have to supply power and ground to the pins from an external source if you remove the instrument cluster from the motorcycle and try to bench test it.