[chicagokevin]

I'm rebuilding a '72 K5 CB450. After putting everything back together all of the electric worked fine and bike started, then, suddenly...bike died and starter button did nothing. The horn also was totally dead. Headlight, turn signals, brake lights, etc. all work fine. Blinking indicator light and backlight for the speedo/tach also work fine, but the neutral light does not.

Came back to the bike the next day and, magically, everything worked fine. Bike started and ran. Skip to last night and same thing happened, bike started then, magically, died and horn/starter switch/neutral light all gone, everything else works fine.

Some research shows these are all on the same circuit and if something goes out it would kill all of them...but where do I start in diagnosing and solving this? I have no electrical knowledge so, while I have a feeling it's either the ground or a bad neutral switch...I don't really know how to prove that or what to do about it. I have the schematic and traced most of the connections and, visually, they all look fine.

I'm 99.9% done with a year long build, and this is the final piece (hopefully), so any help would be SO appreciated.

 

[J-T]

Disconnect the neutral switch and connect the wire to ground. If that causes the neutral light to illuminate likely your switch is sticking That would explain the light and the starter, don't know about the horn though.

 

[WintrSol]

The horn and starter button depend on the ground wire from the bars to the fork top bridge, since the bars are mounted in rubber. There should be a green wire with a large round terminal on it, that bolts to the bridge. You will sometimes get a good enough ground without that wire, but it would vary.

The neutral light gets its power through one of the multi-contact bullet connectors, and you could have a loose connection there, the 4-contact connector for the stator could be loose, or the neutral switch is going bad.

I can't see how the neutral function could be related to the horn and starter button, but loose bullet connectors could affect all three, and they get shifted when you move the bike. You may want to start in the headlamp bucket, and carefully tighten the socket side of the bullet connectors with pliers.

 

[mike in idaho]

Is the kill switch circuit in good condition?

 

[chicagokevin]

Thanks so much for the responses. The bars have been replaced with clip ons, bolted directly to the fork tubes, so there is no longer the ground wire from the top fork bridge. However, since they are bolted to the suspension, I would assume that would serve as the ground. I'll try reconnecting the original ground wire though.

The connections all look fine, how would I go about finding out if one of them actually was bad other than just visually making sure the bullet connectors and wires look intact?

 

[jd50i]

There have been some problems with painted bars not making contact requiring removal of paint to make a ground. Replacing the ground wire is also required.

 

[WintrSol]

Give the wires behind the bullets a tug, to see if the wire is broken inside (pull hard enough and you will break them). Make sure the bullets are a tight fit, and not corroded.

 

[chicagokevin]

The kills switch seems to be in good condition, if it was bad, would it have any impact on the horn?

 

[WintrSol]

No impact to horn; the kill switch only powers the coils.

 

[chicagokevin]

So I spent some time on the bike this weekend...and discovered something very bizarre. A video is below. As mentioned above, the bike will run and then goes dead and the starter button, horn button and neutral light all go out. I discovered that if I unplug the two wires going to the horn and directly connect the ground (green wire) to the frame/engine, then take the lead wire (black) and first touch it directly to the negative terminal of the battery, and then the positive terminal of the battery, it "resets" everything and the bike works fine. Horn works, starter works, neutral light work. I can then start the bike and it will run for a short time and then go dead again with the same issues with the starter/horn/neutral light.

What could possibly be causing this?? The bike is stock, other than a SparcMoto regulator/rectifier and a brand new ignition switch.

I doubt this has anything to do with the horn, it was just the simplest piece to isolate. It must have something to do with the grounding, or maybe the charging circuit?? I'm at a total loss.

 

[WintrSol]

I wonder if the ground cables from the battery are good; clearly, the one that grounds the headlamp is OK, but the one that provides the ground to the starter switch and horn button is not. Since the latter get ground through the frame, and not the harness, I would suspect the heavy cable from the battery to the frame/engine mount. Maybe just a good cleaning of the battery and frame terminals would make a difference; if that was done, next on my list is corrosion of the cable itself.

 

[chicagokevin]

So this seems to have been solved by sanding off the powdercoat between the ground wire to the battery terminal, the frame bracket it it attaches to, and the frame and engine. I also discovered that the green ground that attaches directly to the battery had a a break around the ring connector. I attached a new one and all is running well. Thanks everyone for their help.

 

[WintrSol]

Thanks for posting the fix. Wish all problems were that easy.