I have a similar problem with my 86 fourtrax trx350, but my issue is when removing the corrosion from the contacts inside the switch (again), the outer switch housing discombobulated and is not going to go back together.
Ont he trx350 it shows that off 2 wires get shorted (the engine kill) and when on the other 4 get shorted (in pairs). My wife needs to still be able to use the electric start to get it going so I was thinking of installing 2 switches to short those wires. Unless someone can give me a better idea of if both sets need to be shorted, or if I can get away with just one pair? And would it work to just de-solder the wires from the back of the switch and then put them on the newly installed switches? Or would I need to go down to where the ignition switch connections are in the fender?