{"id":42701,"date":"2019-09-28T17:55:50","date_gmt":"2019-09-28T08:55:50","guid":{"rendered":"https:\/\/www.decoboco.info\/en\/?p=42701"},"modified":"2026-09-24T13:45:14","modified_gmt":"2026-09-24T04:45:14","slug":"mysterious-fuse-blowing-z750ltd","status":"publish","type":"post","link":"https:\/\/www.decoboco.info\/en\/20190928\/everyday-events\/mysterious-fuse-blowing-z750ltd","title":{"rendered":"Mysterious fuse blowing on the Z750LTD"},"content":{"rendered":"
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The other day, the starter button on the right switch broke off, and after replacing the switch, the fuse would occasionally blow.
I thought maybe I made a mistake when swapping the right switch, but the cause was unclear\u2014it would happen sometimes and not others.
What on earth? <\/figcaption><\/figure>\n\n\n\n\n\n\n\n
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The other day, the start button on the right switch broke off. Well, it’s been over thirty years, so some deterioration is inevitable. <\/figcaption><\/figure>\n\n\n\n
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I mean, I’d never seen one break like that before. Since the original part is discontinued, I decided to use one from a PMC Z750FX-1 or similar. <\/figcaption><\/figure>\n\n\n\n
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The switch shape is almost identical to the original, and it has the same six wires.
A simple setup with just light switch, kill, and starter.

The wire colors on the switch side differ slightly from the original, but I checked and installed it correctly.
Now that I think about it, the fuse blew around this time. Looking back, that was strange.

At that point, since the bike was old, I also got a request to replace the ignition coil. <\/em>

About a month passed due to my work schedule, and when I did the coil replacement the other day, the owner mentioned the fuse had blown before but hasn’t blown since.

Could it be the handlebar switch? I checked again and test-rode it\u2014no problems.
We decided to just monitor it for now, but a few hundred meters after leaving the shop, the fuse blew again, so we made an emergency pit stop.
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I don’t have a cartridge fuse on hand, and if I keep swapping fuses every time one blows, there’s no end to it. So my strategy was to solder a circuit breaker fuse <\/a> as a test tool.

There are different types of fuses: fast-blow fuses <\/em> ( fast <\/em> blow), normal fuses <\/em> (normal blow), and time-lag fuses <\/em> ( slow <\/em> blow). It’s good to use them according to the application.
I haven’t looked it up, but I think this circuit breaker type is probably super slow. <\/figcaption><\/figure>\n\n\n\n
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Without the symptom showing up, there’s nothing to work with. I need to test-ride and figure out how to make it happen.
I drove around in circles, and sometimes the main 20A would blow, sometimes the 10A, and sometimes it wouldn’t blow at all\u2014frustrating.

But when I think back to when it did happen,
it was on hills, especially going uphill
or in first gear with the throttle on and off, jerking the bike
or accelerating hard from a traffic light.

Odd situations. I’m not turning the handlebars or operating any switches.
I figured the fastest way was just to check everything. <\/figcaption><\/figure>\n\n\n\n
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I disconnected every connector and terminal from head to tail to check them. <\/figcaption><\/figure>\n\n\n\n
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I had to degrease every visible spot and inspect each one individually. <\/figcaption><\/figure>\n\n\n\n
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If there were no problems, I wrapped them with acetate tape <\/a> for safety. <\/figcaption><\/figure>\n\n\n\n
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The headlight rubber was missing, so I installed that too. <\/figcaption><\/figure>\n\n\n\n
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Wait! A discovery? Maybe? This shriveled condition. <\/figcaption><\/figure>\n\n\n\n
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But there was no break or burn, so it wasn’t related. <\/figcaption><\/figure>\n\n\n\n
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I also checked the main ground just to be sure. <\/figcaption><\/figure>\n\n\n\n
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It’s good to strip a layer off the block side too for peace of mind.
But I’ve only experienced a fuse blowing due to poor ground connection once in the past, so it’s actually pretty rare. (If it’s original.) <\/figcaption><\/figure>\n\n\n\n
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Checked all harnesses and protective covers
Checked main ground
Temporarily swapped the right switch for a different one

There’s no way it can blow now! I thought, so I mounted a GoPro and headed out to Odaiba for a test ride, feeling cheerful.
But right as I was driving on Route 7, I heard a click\u2014the breaker tripped!
After resetting the breaker, the symptom didn’t come back. This is frustrating.
Wait a minute. The switch is aluminum… could it be? <\/figcaption><\/figure>\n\n\n\n
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When I removed the left switch, the screw was missing\u2014and it was inside the switch! This has to be it. To simulate it…
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I’ll test it. First, I’ll ground the 22.2 mm terminal. <\/figcaption><\/figure>\n\n\n\n
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Tighten it securely with a co-fastener. <\/figcaption><\/figure>\n\n\n\n
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I’ll try grounding it here, then put the cover on and shake the switch!
It blew! And I even reproduced that weird symptom of flickering on and off. This was it!

So that’s why it would blow on hills or when I jerked it in first gear. Absolutely unbelievable. It’s been good material and experience, but the video of it failing will be on YouTube. <\/figcaption><\/figure>\n\n\n\n
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I also replaced the fuse with a blade-type one. Classic Honda move. <\/figcaption><\/figure>\n\n\n\n
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I fabricated a bracket to secure the fuse box. Naturally, it’s nut-free with good removability.
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I painted it black with gun coat. <\/figcaption><\/figure>\n\n\n\n
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Safe even under suspension! Easy access! Once the side cover is on, you can’t see it anyway! So this was the only spot. <\/figcaption><\/figure>\n\n\n\n
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So the invisible modernization progressed like this. <\/figcaption><\/figure>\n\n\n\n
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Since there are only three circuits, it looks like this. There’s an odd gap due to the wiring layout. <\/figcaption><\/figure>\n\n\n\n
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In the end, it all came down to coincidence and deterioration:
the starter button came off
a bolt inside the left switch fell out at some point <\/em>
symptoms started appearing right after I replaced the right switch
and the fuse would blow from impacts on hills and bumps.

Usually, the area I touched is the culprit, but this time I was completely blindsided by an unexpected troublemaker over two days.

You might think, “This makes no sense?” but you can’t give up\u2014you have to eliminate the mystery one step at a time.
I wouldn’t want to experience it again, but now that it’s over, I think this kind of thing is actually pretty interesting.

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