I'm not convinced. The pickup is a hall effect switch operating in a magnetic field. It does not see the field. No current is induced in the hall effect switch by the magnetic field of the alternator. The switch is running blind and smooth until it approaches and runs across the copper shielding and hits the magnet. The magnet is a "bump in the road". That bump induces a voltage/current read by the box. The screw heads would be a hole in the road possibly N. . Magnet should be south pole facing out as most switches of this type work on the South pole. I don't know, I'm just saying.
"....I suspect the magnet is placed so it is opposite the magnetic field of the rotor." I'm betting your right!
I'll almost bet money, that when we think the magnet has lost it's strength it's really the pickup winding degraded. By putting in/on a stronger magnet gives the degraded pickup a new lease on life. Quickest way I know of to kill a magnet is hit it or drop it. But I'm not a one-wire, so I don't know.
"....I suspect the magnet is placed so it is opposite the magnetic field of the rotor." I'm betting your right!
I'll almost bet money, that when we think the magnet has lost it's strength it's really the pickup winding degraded. By putting in/on a stronger magnet gives the degraded pickup a new lease on life. Quickest way I know of to kill a magnet is hit it or drop it. But I'm not a one-wire, so I don't know.