Yes. Bad connection. Battery good. Wires/connections/grounds not good. Seventeen year-old scoot. Gotta be loose or corroded connections all over.
Disconnect battery, ground (-) (black) wire first, remove any body panels necessary to inspect the ENTIRE wiring system. Disconnect EVERY connection (whether plug-in or nut & bolt), inspect, clean, coat with silicone dielectric grease, reconnect. Wire brush or remove rust from any/ all ground points.
Please report findings here and definitely ask questions here if in doubt. Pay particular attention to any remarks by a guy named "Ruffus." He does this stuf for a living and knows what he speaks.