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Discussion Starter · #1 ·
the 10A fuse on my headlight circuit has recently started blowing. When I replace it it works for maybe 2 or 3 rides, then blows the fuse. It's been a little intermittent so sorta tough to trace down.

I do have a DMM but am admittedly new to using it but know some basics.
Anyone have a few tips on certain connections I might start at with the multimeter to try and narrow this down a little?

Planning on checking the hi/low beam switch for corrosion,
and the current flowing through the fuse for a start.
(it is breaking the actual wire inside the fuse, when they pop I can see the wire inside failing which tells me too much current?? lose ground?? frayed wire??)

any tips appreciate !!!!
 

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Check the wires going through the steering head area that they havent broken and shorting out on the frame.
 
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When the fuse actually blows it is due to high current. High current is almost always due to a short circuit. A short circuit will occur when a wire conducting electricity touches a ground, the frame for example.

To track down a short circuit replace the fuse with a 12 volt light bulb. The bulb will light when there is a short circuit. Try moving wires to see if you can cause the short or cause it to go away if present.

Look for wires where you can see bare wire, insulation worn away or melted or chewed by rodents.
 
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Discussion Starter · #4 ·
measured 13.4v across the fuse location... same at battery direct. I wouldn't think that would blow the fuse ?? I'll keep searchin :)
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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measured 13.4v across the fuse location... same at battery direct. I wouldn't think that would blow the fuse ?? I'll keep searchin :)
Voltage doesn't blow fuses. Amperage does.
 
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Do what reclinedrelic said with a light bulb. It should light when the headlight is turned on but won't be full brightness unless the short is present The bulb should be an 1156 or something similar (too small a bulb can have confusing results because it has much higher resistance than some normal loads). Don't worry about not having a fuse in the circuit when you connect the bulb because the bulb will limit the current to a safe level.

Re learning how to use your multimeter: A multimeter is basically a number of meters for measuring different things combined into one so it is best to learn what each type of meter does first and this page has a good explanation of that. Once you have read about the various types of meters click Multimeters near the bottom for the page on how to use them

This page on what series and parallel circuits are and how they work is also recommended reading
 

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Discussion Starter · #8 ·
Thanks so much you guys are always so helpful! Really appreciate your expertise.
AND... I think i might have found the guilty party... This would do it I would imagine... It was resting against the bottom of the lower triple, and it's in the headlight circuit. (see below image)

Automotive tire Light Coil Motor vehicle Hood


Product Rectangle Slope Schematic Font
 

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Ideally, you'll get a couple layers of heat shrink on each of those. That will involve clipping and rejoining the wires.
At least wrap each wire with self-sealing silicone tape.
 
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Something has crushed those two wires. While you are repairing them figure out what caused the problem in the first place and fix that too. They may be getting pinched when the steering is at its limits.
 

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Had the same thing a couple of years back.

Wire was caught in the steering lock for me though. So it was a bit more obvious to me, as the light stopped working when I turned left..
 

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Yah....i had a Bmw where the ignition would cut out each time the bars would turn....eg going roundabouts or sharp corners...the rider roadside assist wouldnt help cause they said the bike was RIDEABLE...
Ended up being a frayed wire at steering head...5 min fix...
 

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Discussion Starter · #14 ·
Something has crushed those two wires. While you are repairing them figure out what caused the problem in the first place and fix that too. They may be getting pinched when the steering is at its limits.
Yessir! exactly right. Got stuck in the turn stop I'm guessing. I since wrapped it and rerouted it so that wouldn't happen again.
 

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Yah....i had a Bmw where the ignition would cut out each time the bars would turn...
The Grub was doing the same a couple years ago. There was a kink in a wire inside the main harness just behind the steering head. No wear on the insulation, but each time the handlebar was turned hard left, the wire would flex at the kink and fray a little more.
Finally, it gave out completely while I was searching for the fault. I spliced in a short piece of new wire, heat shrinked and rewrapped, and all is good.
 

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When I searched “Roadside Assist” on my phone it only returned my own number. 😆
 
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