Topic: Horn and Charging Issue '74 CB550 - Technically inclined Newbie needs help!

[davidru2]

This is my first post - just acquired my CB550 a few months ago and its had a charging issue ever since I got it.

-Replaced battery, previous owner had put a new rectifier on just months ago, but after 3 days with a fresh battery it goes dead.  I'm going to dig in deeper with a multimeter to see if I can find any issues withing the starter or rectifier, but when I look at voltage on the battery while I rev the bike it seems to do what it should... Volts go up to 15 or so when I rev.

My other issue is the horn.  I checked and the horn does work, it started out where I just had to keep tapping the button hard and repeatedly to get it to fire, but now it just died.  After disconnecting the horn my multimeter only gets a very weak .50 reading when I press the button, could this be a switch issue?
My assumption is that a switch either works 100% or not at all.  I assume I should see close to 12 volts from these wires after pressing the button.


Thanks!

[calj737]

If you're getting 15v at the battery, then you're badly overcharging the battery. It should never see more than 14.4v at any rpm range. Best to replace with a correct unit.

The horn button should be creating a ground to the horn circuit. It's powered by BLACK so pushing the button closes the loop. You can test the horn with a temporary jumper from the horn to frame. Touch the frame, horn should blow. If so, carefully open the switch housing and clean the backside of any corrosion and verify that your housing is contacting a good, clean metal bar. If the bars are painted, it can interfere with good grounds.

[Deltarider]

What horn is it? Stock? Check the wiring scheme in the Owner's Manual. Wiring differed for various markets (area code!). If the wiring is like Calj suggests, his test is easy to do. If you have a horn like mine, you'll need a relay for sure. Without it the switch will be gone soon.

it started out where I just had to keep tapping the button hard and repeatedly to get it to fire, but now it just died.  After disconnecting the horn my multimeter only gets a very weak .50 reading when I press the button, could this be a switch issue?
My assumption is that a switch either works 100% or not at all.

Not quite, if the switch isn't up to it and develops burns, it will build more and more resistance. I'd say in your case it looks like that. But corrosion can also cause it.
If you read 15 V, it could be overcharging but not necessarily. Some DMMs give funny readings. BTW, you did select the right range, didn't you? An analogue voltmeter can give a better result. According to the CB500-CB550 Shop Manual (p.94) max voltage is 14,5. 
That's a nice bike in the pic.