I would bet that you have the wrong dash harness. They where 6 or 7 different ones used originally. I think JD has substituted them down to three. So you will need to get a good wiring diagram and make yours correct.
I would bet that Tim is correct in that you have two grounds going to the dash lights.
Also make sure you have the correct ground/positive at the breakers on the back of the dash door. If you have them hooked up wrong they willmake the dash and lights not work correctly.
It makes it easier If you think of the system as being two separate 12 volt systems. One being negative ground and the other positive ground. Nothing on the whole setup sees 24 volt other than the starter and generator.