For the Tach and service light problems, check the batteries on the SI board first. They are the AA-sized Ni-Cad ones soldered to the board.
However DO NOT use a high wattage soldering iron to remove/install the batteries. It'll fry the board big time. A 10-watt iron should be enough. And make sure the new batteries are charged before installation.
As for the trip meter, just change the plastic gears inside. These can now be found locally and generally made out of plastic suitable for the tropics.