Topic: Left hand control switch is blowing main fuse?

[Geefergie550]

My 76 honda cb550k has recently been blowing fuse after fuse. The main 15 amp fuse. It first started while i was riding and all power cut off while cruising at 35 mph. I wasn't using any accesory switches or on the clutch when it cut out. Had a spare, put it in got almost home then it blew again when I hit the right turn signal switch. Walked home got another spare to make it home. Thank goodness. I began trouble shooting the wiring using multimeter readings and a have narrowed it down to the left hand control switch. I opened up the switch and inspected all of the wires inside. No wire is broken with any exposed copper showing. All the wires are pliable with no stiffness or cracking. So i insert a new fuse with the left hand control switch unbolted any dangling off of the handlebars. I turn on the power at the ignition and it doesn't blow the fuse. I go through the motions of using hi beam and low beam. The left and right turn signals and the horn. It doesn't blow. But what is weird is that as soon as i bolt it back on the handlebars and turn the key to the on position, it blows immediately. Tried this a couple of times and have now gone through 7 fuses. 3 were on the day this problem presented itself. And 4 by diagnosing and tracking down this problem.  There are some pictures showing some questionable areas inside the left hand control switch that might be the culprit. One is the solder joint underneath of the left and right hand turn switch. The solder is touching metal. The other is the plate that holds the loom against the inside of the casing. The screw will not tighten enough for the plate to have clearance of the handle bar once bolted back on. The plate touches the bar . Any advice help would and be much appreciated.

[Don R]

  If the wires are run inside you may have a scuffed wire inside the handlebars. I'm not sure on a 76, If outside unwrap them and find the pinch.

[Geefergie550]

I have unwrapped the loom. No pinched wires

[Kevin]

Have you checked each wire for contuniuty (no resistance) to the switch housing?
That'd be my first step of troubleshooting.

Sent from my SM-N960F using Tapatalk

[HondaMan]

A question that might seem unrelated: are you using the glass fuses, still?
Reason I ask: the type of fuse needed is the SFE. This looks like a wide piece of tinfoil inside the glass tube. They have not been made at all since 2002. Only a few were made after 1997. The ones you get now are instrument-grade, or if using the ceramic-case type they are appliance grade, neither made to operate with vibration. When they carry current they get soft and flexible, and a bump can break them at that moment, making them look like they "blew" for no apparent reason.

Here is what complicates this: the clips on the fuseholder are (were) plated with chromate, which was a 10-year life product. Today it has lost its grip on the metal clips, and it makes an effective heater when the fuse passes current to it. This heats the weak fuse even more, and makes them melt easily.

Here's how you can test if yours is causing 'blows' for no apparent reason: if you have a gun-bore brass cleaning brush in .22 caliber size, or one of the small round metal brushes form the Harbor Freight assortment of brushes, spin it inside the fuse clips to clean away the chromate plating that is falling off now. When it shines again, reinstall a fuse and try your tests again. There might not even be anything wrong with the bike itself.

If that solves it, I can make a new fuseholder for you that uses modern ATC/ATO blade fuses, which will let you find the correct fuses everywhere (even the grocery store!).

[enwri]

Is that soldered connection touching the arm?