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Hi everyone,

So I've burnt my wiring harness half a year ago and finally managed to get the wiring harness replaced and the scoot running last month.

I thought i'd be good for a long time now, but just yesterday when my bike accidentally toppled due to uneven ground (and I let it down lightly), the wiring harness burnt up again. I've heard all about the pet carrier causing the wiring harness to get pinched in the engine compartment so I didn't use the pet carrier again, but the wiring harness burnt up at the same places as before: right under the front of the seat.

Why did this happen? I can blame wear and tear on the first time round, but the second time round the same thing happened. Can anyone enlighten me on this? I simply can't understand what's going on.
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UTC

Molto Verboso
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@der_blechfahrer avatar
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Did you perhaps re-use the connectors?
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Der Blechfahrer wrote:
Did you perhaps re-use the connectors?
Entirely new wiring harness, no connectors were re-used.
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I may be way off base, but my first thoughts are either something is drawing way too much current, or some ground somewhere in the system isn't connected, just my two cents worth
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Was this a brand-new harness, or second-hand? And did you use dielectric grease on the big three-way connector to protect it from corrosion and poor connection? That connector has caused several fires before, as reported on MV, and should always be given a quick inspection once in a while to ensure there's not the slightest sign of over-heating. It carries the highest continuous voltages and currents in the whole system.
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hard to tell in the pics what could be the issue.

bad ground
pinched wires
improperly routing of harness making it too tight, not able to flex when the engine flexes.

rubbing against a bolt
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correct me if I'm wrong, but didn't you have several aftermarket electrical components that you've added to the bike?

if so, how were they tied into the electrical system?

second, for something to light up from such an innocuous mishap leads me to believe that the harness or some part of it, or something added to it, was not routed properly and left exposed.
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jimc wrote:
Was this a brand-new harness, or second-hand? And did you use dielectric grease on the big three-way connector to protect it from corrosion and poor connection? That connector has caused several fires before, as reported on MV, and should always be given a quick inspection once in a while to ensure there's not the slightest sign of over-heating. It carries the highest continuous voltages and currents in the whole system.
Thanks jimc, the harness is brand-new and I did not use dielectric grease anywhere. Which big three-way connector are you referring to? I'll take a quick look again later.
⚠️ Last edited by ilovecats3000 on UTC; edited 1 time
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old as dirt wrote:
hard to tell in the pics what could be the issue.

bad ground
pinched wires
improperly routing of harness making it too tight, not able to flex when the engine flexes.

rubbing against a bolt
The ground cable was bolted onto the frame, how do I tell if it was a bad ground or not?

Pinched wire and improper routing is on my mind as well but given that the wiring harness is new, I'd expect a different outcome from my old wiring harness but it's exactly the same...so I was wondering if it could be something different.
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ilovecats3000 wrote:
Thanks jimc, the harness is brand-new and I did not use dielectric grease anywhere. Which big three-way connector are you referring to? I'll take a quick look again later.
The one under the seat hinge, that carries the 3-phase current from the stator to the regulator. If you kept the same regulator and its connector from last time, a poor connection there become even more likely.
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greasy125 wrote:
correct me if I'm wrong, but didn't you have several aftermarket electrical components that you've added to the bike?

if so, how were they tied into the electrical system?

second, for something to light up from such an innocuous mishap leads me to believe that the harness or some part of it, or something added to it, was not routed properly and left exposed.
I have 2 horns and one contactless payment device on the scoot. I connected only one of the horns and left the other one alone. The contactless payment device had its own cable routed to the battery directly. There was no damage on that cable and it draws 0.45mA constantly.

I made no modifications to the wiring harness itself. Since its entirely new I'm not expecting anything to be exposed as well but the only conclusion I can come to so far is something melted/rubbed against some part and caused it to be exposed.
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jimc wrote:
The one under the seat hinge, that carries the 3-phase current from the stator to the regulator. If you kept the same regulator and its connector from last time, a poor connection there become even more likely.
The regulator was swapped as well. Could you be referring to the white connector in the picture below by any chance?
Forum member supplied image with no explanatory text
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Yes.
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jimc wrote:
Yes.
Dielectric grease was not used on that connector, but it's been less than a month since the harness was replaced. Are you saying that because I didn't use dielectric grease on that connector, the wiring harness burned out? How is the connector overheating? I usually ride between 30-60mph on the scooter and I don't ride for more than an hour at a go.
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ilovecats3000 wrote:
Dielectric grease was not used on that connector, but it's been less than a month since the harness was replaced. Are you saying that because I didn't use dielectric grease on that connector, the wiring harness burned out? How is the connector overheating? I rarely go over 60mph on the scooter.
It can happen at idle! It only takes one of those connectors to make poor contact and it'll heat up. That starts a vicious circle, with the contact going higher and higher resistance. We're not talking high numbers here - just 0.5ohm will produce 10W of power when 20A goes through it. That enough for a connector to expand and get worse and worse very rapidly. Eventually the insulation melts or catches fire, and the stator output gets shorted to chassis. Then the flames really get going...

Now, it may not be that in your case, but it's been an oft-reported failure here on MV.
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