Possible Battery earthing issues...HELP

[Dannyorrill]

Hi, I am having trouble with my 2007 Yamaha Cygnus x (nxc) 125cc and am hoping somebody can help me out here.
I went out to start it the other day and got no response no lights no noise nothing, so I assumed this would just be a dead battery.
Today I fitted a new battery to the bike and she started straight away however, my rear brake cable and lever were very hot to the touch almost as if the cable is carrying and electric current?? I could also hear a slight noise coming from my battery it’s self so I disconnected everything as soon as I could.
My guess was a bad earthing but at quick first inspection all seems well.

Has anybody had similar problems?
Any help is much appreciated.
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Danny

[Kawasaki Jimbo]

That's a handlebar lever, isn't it? You'd need quite some current to heat that chunk of metal. Peripheral neuropathy?

[steve the grease]

Its an earthing issue between the battery and the engine. There should be a good earth connection to the engine, cos I guess it's rubber mounted. Either the wire is busted or maybe where the brass terminal bolts on to the alloy engine is corroded (most likely) Steel bolt, brass terminal, alloy casting, not a good mix. Undo the terminal ( prolly 8 or 10mm) on the engine end and clean the corrosion until the alloy and the wires terminal are shiny. A little bit of grease or vaseline and do it back up. Sounds like the connection to the handle bars is ok , what about the connection to the frame itself?

[Dannyorrill]

I have cleaned up all terminals and contact points yet the problem is still there!! The cable itself looks in decent condition. ! Within 10 second of connect my battery my brake line from the back wheel right up to the handlebars is red hot... any other explanations for this happening?
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Danny

[Nobby the Bastard]

Disconnect the switch for the brake lights. I suspect that the power is being shorted from the switch to eath via your brake line (I.e the switch is fucked)
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050

[Dannyorrill]

Tried disconnecting the brake light switch from the bars however the the brake line is still carrying an electrical current? I’m guessing it drawing it off the engine maybe??
This has me baffled 🤔🤔
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Danny

[Nobby the Bastard]

Check the earth strap from the engine to the frame.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050

[Easy-X]

Yeah, I just had this on my scooter, exactly as Nobby suggested. Mine loose wire was on the crank case cover so you'll either have to pull off some inspection panels or even remove some of the fairings to check over all the wires going to the engine.
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Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[Dannyorrill]

I have taken off all my fairing and plastics already to look for the earth strap. But the only earth I can find is from the battery to the starter motor. (Which I have already checked/cleaned.) going to continue searching today for it. But after spending 2 days looking I am slowly losing hope. 👎🏻👎🏻
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Danny

[Easy-X]

Yes, battery to starter (which is bolted to the engine) and from the engine...

Try going at it the other way: find an earth cable from the gauges and switches and trace it back. You should find something that goes under the bike and towards the engine.
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Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[Dannyorrill]

Ok so I tried to trace back an earth from the switches as you’ve said But the only earth I can find is still the one to starter motor. I’m almost certain there is not another running From the engine.... think the only thing I can do is remove the whole wiring loom in search of the elusive earthing strap
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Danny

[Easy-X]

If I'm reading you correctly the earth wire(s) from the front of the bike meet up with the earth side of the starter motor like this?

Battery ------> Starter

Gauges -----> Starter

Or is it the case you haven't found the route? I wouldn't blame you there: a mass of black cables is hard to decipher.

On my scooter, when the earth strap was flapping about rather than attached to the valve cover, it would occasionally start and then things like turning on the indicators or pulling the rear brake without the switch connected stalled the engine which sounds very similar to your rear cable carrying current. (Bear in mind that most likely the only cable that runs completely from front to back of the bike is the rear brake cable.)

Well the other approach is to break out the multimeter and check you have continuity between the battery earth and various random items on the bike... regulator/rectifier being the first place to start. Having a wiring diagram would make the task much easier.
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Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[Dannyorrill]

Yes I am struggling to find the route. The only earth to the starter is from battery. And yes a wiring diagram would be extremely helpful amcurrently searching for one online. Hopefully the diagram will point me in the right direction. I would have assumed that it would have been reasonably accessible/ visible but like many things on the bike it’s probably a poor design.
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Danny

[Nobby the Bastard]

How about just getting a nice thick gauge bit of wire and bolting it to the engine and frame and seeing if the problem goes away?
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050

[Dannyorrill]

Yes think I may have to give that a try and see if it solves the issue. As still unable to find it. However I did find what I believed to be an earth strap but it only goes from the frame (front of bike) to the petrol filler cap..... I also tried to trace back the earth from the starter relay and had no luck of finding it as yet.
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Danny

[McHattrick]

Hi Danny
Is this your bike manual?
https://www.manualslib.com/manual/983364/Yamaha-Xc125.html
Other manuals available on this site if not.
I would have thought your problem could be a short from +ve side.
Could even be through the relays.
On the circuit diagram from above, looks like you need brake 'on' to run starter moter?
Item 33 is starting cut-off relay - worth checking - and this, if working should energise item 34 (starting relay) if brake engaged.
Thats if I have read it right.
Worth testing these relays.
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If it aint broke... fix 'til it is.

[Dannyorrill]

Problems solved!!! It was a loose connection. Tightened it up and all seems to be well now 🤞🏼 The help has been much appreciated lads. Cheers.
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Danny

[Easy-X]

Great news, always satisfying to fix it yourself
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Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter