trx300fw dies whennput in reverse.

I have a 1990 honda trx300fw. it was a barn find and has been sitting for 20 plus years. owner said it had less than 15 hours on it. it didn't have spark and I bought a cdi box and new coil. that didn't work. bought a new rectifier and that didn't work. bought another cdi box and now I have spark and it runs, the first cdi I bought was not the right one apparently. now when it starts the reverse light is lighting up and when i put it in reverse it dies. i also noticed that the kill switch does not work. i dont know if that is related or not. any help would be appreciated.