Get a volt/ohm meter and start looking for a short in the wiring. see where there might be a completed circuit between the 30 amp fuse and the light circuit. Could be many places in the harness.
Mine was shorted between the ignition hot lead and adjacent 18 guage wires in the main harness. It happened because it was overheated when the previous owner tried to jump start the bike with a car battery.  I had to open up the main harness and replace the melted wires.

I occasionally check in here to update anyone who cares about the current status of my 2004 GT 250. I own 4 other much fancier bikes and over the years have owned dozens of others and I really believe the GT250 to be highly underrated.

I have owned mine for about a 13 years, and I am ashamed to admit that I have put a grand total of about 40 hours of maintenance into this bike (i.e a MAYBE three hours a year), and yet, it continues to reward my gross neglect by running pretty much like the day I bought it. 

I generally abandon it every winter and don't do ANY of the storage steps that I should be doing (and generally DO perform for my more expensive but less reliable bikes) but sure enough, every spring I drain the old fuel out of the GT, fill her up with sea foam and let her sit for a day, drain her again, put new, clean fuel in and sometimes a new battery, and what do you know, she starts first time. After a quick few safety checks, she's ready to drive and asking where I want to go today.  First day of riding season I usually have to use her to go get parts and supplies for my other fancy-pants motorcycles that generally won't start for love nor money after 5 months of storage.

Admittedly I don't put a lot of miles on the GT - maybe 2000 km a year, but that bike is the essence of practical transportation. Easy to work on - happy to take cheap generic replacement parts from the local autoparts store if needed, totally adequate performance (especially for a 250, and especially on the freeway). It's my "go-to" bike for errands around town and I have lost count of the number of times I almost took one of my 1000 cc plus collectible monsters out for a ride, but then thought - "screw it... a bird will just shit on it ",  and then took the little GT instead, and probably had more fun and a lot less anxiety about reliability as I trust that little bike completely. 

The only issue I am seeings is that over time the electronic fuel gauge has gradually stopped working. Do I care? Honestly not really, but if anyone has any tips for an easy fix or replacement strategy I guess I might give it a try one day.

I can also foresee that eventually the cheap original exhaust will rust through and I will probably need to replace it. Anyone got suggestions and pictures for an economic after market solution?

Hey,

Okay while ridding i noticed i was getting some vibration from the back and on inspection i noticed 1 of the pistons are seized up on my caliper not letting it retract and is demolished the disc, so im needing to replace the rear caliper and disc, problem is there seems to be a to of calipers that fit on ebay but look nothing like the 1 on the bike, does any 1 know where to get a quality replacment even possibly and upgraded caliper? Any help is much appreciated.

Ps. I got the naked model which has the single disc front on the left side of tire,  and i would like to get the right hand set to upgrade it to dual disc, any 1 got any experince in attempting this?

Don't know for sure but Roadster cycle  has a plug and play replacement for the 650. It's a Shendigen. It may work on the 250 as well.

Hi there! Interesting question, unfortunately, I don't know how to do it but I also heard that there are people who can hit around 100 kph. Personally I have  2004 Hyosung aquila gv250 in a garage of my property in Spain, waiting for better weather to drive it around more often.