Get a wiring diagram for the skis and apply to the boat. I did the same for a 94 speedster and did a write up on it here on the board. Not sure how much it will help with the 99. Wasn't really that hard, but you need to pay attention to details and make quality waterproof connections. Some functions you won't need to mess with are lighting, bilge fans, radio, bilge pump, fuel level. Just focus on start, stop, charge and dess systems.