Hey Pete!
Great questions there. Hope this answer helps!
- ALL “GT125” since 1998 use the same coils , same CDI , same regulator.
- They started with a small grey regulator –> then they tried a slightly bigger black regulator a few years later (since 2010 i should say)
(but both fail too much!) They can’t even do 14.6 volts! - They tried to use a newer coil from a 250-EFi (which also works with Carb bikes)
However, no power difference whatsoever.The upgraded reg/rec uses MOSFET tech regulators, which are much more efficient than 1970’s serial/diode tech (Hyo). Very common on big Kawasaki machines, so you know the Japanese don’t like for things to fail.
And I know Kawasaki machines myself, so i studied their electrics in comparison to hyosungs. For example, I would know which pins are plus / negative , how much volts per wire etc…
650 owners = 2 major mods they always do = Drop a 250cc Ninja Magneto & Regulator as the 650s REALLY do cook their stock regulators , so an upgrade was necessary. Hyosung would just keep on sending the same stock ones which would again blow up. No change.
125ccc = All standard hyosung regulators cause so many problems, it’s beyond belief. Just go on our facebook group, also chinese versions have set the bikes on fire & smoke on dashboards.
So I never ever sell them, (too much liability) – Kawasaki tech wins.
Wiring Harness = 125GTR / GT125 Nakeds (all) – Same plug, No change whatsoever.
Ignition Coils = Also a bolt on fit , just look at the shop gallery, so many bikes 2007 plate , 2016 RC , 2012 model etc… Kawasaki race parts here again.
People tried Suzuki SV650 coils on 125, they don’t work. Placebo effect lol.
Remember, no one goes to a mechanic under my watch, I got you! –
For a total novice biker Even clutch change was done at home without paying a random mechanic £200 to do it!
Oh by the way! – It’s a great shout check your spark plugs , if they are the “stock ones” (CR8E) – Just bin them. Too heavy & fouls too much.
“CR8E IX” (Blue iridium) or CR8E-Lasers work best! – The coils & reg rec work best with IX or Laser plugs definitely.
Remember, this colour below = a very happy hyosung motor (Good sparks, fuel, air)
(All coffee brown ring/dark biege center)

If there is anything i missed, just let me know! Have a great weekend.