Bike won't start... Short-circuit sound!

[_The_Roof_]

Hi guys.
I'm new in this forum, I'm sorry for some errors that may appear...
I have a 1999's GZ250 and lattely I had some problem starting up the engine...
The battery is probably dead, I'll get another one, but the latest problem is on the starter relay. I started earing a short circuit sound from battery lead wire or motor lead wire, I'm not sure which one (I'm noob, I'm telling by the manual images...) when I try to fire it up. Tried to disassemble the battery and starter relay and saw that the contacts had been in contact with rain and they were all with rust (?) around the 20V fuse. Changed the fuse, tried to eliminate the rust but the noise is still there.
Tomorrow I'll try to post a video and some photos here so you can give some advice.
I live in Portugal, I don't know if the European GZ250 differs from the American ones...

Another thing, how can I eliminate the rust from the rims and some screws on the bike? Any special product?

Thank you very much,
João Pinto.