I've been working on my lovely '74 3 & 1/2 Sport for a few weeks now trying to put it back on the road after a four-year hiatus.
Its coming together nicely EXCEPT that I've stumbled into some bizarre electrical conundrums for the first time in the last 32 years with this bike.
I need some help here, so please read on, oh wired ones.
1) The horn used to bellow that particularly assertive Fiamm honk that instantly distinguished this machine from the myriad Japanese weenie horns out there. Now, it barely emits a choked-off kind of toot that would never pass inspection, never mind alerting some dozing numbskull to the proximity of another driver. When I wire it hot to the battery terminals, it screams as it should. I've removed and cleaned all spade contacts and the ground, and also cleaned the handlebar switch while on the lookout for any obvious signs of corrosion. Get this: when the horn button is depressed, the tach needle bounces about 500 rpm or so.
2) The flashers ceased to cooperate, so again I traced through the loom cleaning all contacts, etc. It seemed that the relay (CEV 12v 42w Intermitenza) might be the culprit. Unable to conveniently locate a direct replacement, I scored locally a Wagner #537 12 v 3 terminal unit, and, problem solved. That is until one turns on the headlight or activates the brake light, and then the flashers stop. Once the other lights are turned off, the flashers will not re-engage unless I first put the switch back to the center position and again switch them on from there.

3) Happy ending (so far) to this one: When the headlight was turned on, the application of the brake lights dimmed the tail light. I switched the two (non-ground) connectors on the tail light and the operation went back to normal. Cheers.
4) The small switch operated by the front brake lever seems to operate sporadically. (Touching the two leads directly operates the brake light flawlessly.) Perhaps the switch is beat and should be replaced. It IS over thirty years old, and the bike has over 30,000 road miles on it so far.
Any helpful suggestions on how to proceed from here would be most welcome. I a bit of a dunce when it comes to electronics, so please be kind!

Regards,
JohnnyLaw