Hi, Anonymous in the back of the service manual is a wiring diagram otherwise the usual suspects are:
1. Fouled spark plugs.
2. Severely discharged or a damaged battery should have 12.5 volts or more and be able to pass a proper "LOAD" test if necessary, you may have a preliminary reading of 12.5 volts or more but little or zero amperage the battery is faulty and must be replaced, AGM batteries fail in this scenario more so than lead-acid batteries.
3. Check battery terminals for damage or corrosion, check the battery cables at "BOTH" ends for loose, corroded, or broken connectors, "INSIDE" and outside the cable harness, perform connector wiggle test and check cables with an ohmmeter if necessary.
4. Loose connection at ignition coil or plug between ignition sensor and module.
5. Spark plug cables in bad condition, shorting/leaking, spark plug cable connections loose check for spark leakage in the dark.
6. Faulty ignition coil or electronic control module.
7. Faulty pulse coil.
8. Faulty CKP, CMP, or BAS sensor.
9. Faulty ignition switch.
10. Tilt sensor needs a reset.
11. Security alarm failing to disarm needs reset
For more information about your issue and valuable "FREE" downloads that you will need for viewing or printing please click on the blue links below. Good luck and have a wonderful day.
2005 Hyosung GV250 Aquila wiring diagram Google Search
Need help with no spark issue
Hyosung Aquila 250 Service Manual
HYOSUNG GV250 User Manual