Find attached some info. from the old "tech section" of what is now trialspartsusa.
Don't know if it will help, but it discusses how to test the coil and stator, among other things.
I think you will really like that bike when you get it going! I have an '01 TXT 321. It is lots of fun and has great, "un-stallable" power. The 280 will be similar, I believe, and makes a very good tight single-track trail bike.
Have success!
Jeff
TXT Electrical Information PDF.pdf