Motorcycle Questions? Ask a Mechanic.
Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, please post back with clear pictures of the "... magnetic switch..." / starter relay and the bog cables to its 2 large terminals.
Still, proposed preliminary tries (if have not been done) would be to confirm that the battery cable is connected to the big B terminal of the starter relay while the cable to the starter motor would be to the M terminal. If unmarked, then try to swap how the battery cable and the starter cable are connected to the 2 big terminals of the starter relay.
The starter relay also serves as the main fuse and distribution for the B+ hence it would have to be re-checked. The battery cable goes to a big terminal of the starter relay and supplies +12 to the starter motor when this relay engages. it also provides the always +12 to the main fuse.
Bear with me and consider / try the terminal connection swapping. This would serve as both an attempt of a fix and as a test by process of elimination.