1999 Yamaha G19-ET "ULTIMA" (48V - DC MOTOR) Service and ...
A 1999 48-volt ULTIMA is a G19-ET, and G19ET is the code you should find on the frame plate. Yamaha's service manual for it is LIT-19616-G1-90.
The same book handles 1996 through 2002 and six other cars in the series: the G19-EP, G19-ER, G19-ES, G19-EU, G19-EW and the G19-AX. Fleet operators and anyone who keeps more than one G19 running get the whole line in one place.
The material is procedural throughout. Yamaha sets out the order of work, the inspection measurements and their limits, and the torque each fastener receives. The electrical chapters carry wiring diagrams as built along with the checks to make on the motor, controller and charger, and the troubleshooting sections work from the reported symptom back to the cause rather than the other way round.