2012 NC700X US keeps blowing ILLUM/STOP/HORN fuse

[mistergerf 38]

I was on the highway, for a few seconds the engine ran rough and then the instrument panel quit along with directional, tail and stop lights.  Sure enough fuse had blown, tried to replace it and it blew right away.  Spent a very frustrating Sunday stripping off all the plastic to see if I could spot exposed wiring and a short.  Disconnected the tail light cluster.

 

Rather than blowing more fuses measured the resistance from one side of the fuse to ground - about 3 ohms - a near short.  But I just can't find where the wiring is bad.

 

Is there anything else that could short to ground, like a sensor or some such ?

 

Any tips on finding this problem ?  It's the death of the bike if I can't fix it.

 

Thanks in advance,

Best,

Gerry.

[wjvh 999]

Rear brake switch perhaps ?

[davebike 943]

Usual trickin trade is to unplug everything you can reach that runs off that fuse   fit a resetable fuse   and replace one at a time !
I would suspect the horn or wireing to it  but it much a guess !

Best of luck

[mistergerf 38]

I think I found it ... I got it back on the road today and the MPH readout kept jumping from 25 to 50 to 70 and then after a few miles the reading disappeared completely and the idiot light came on.  That sensor is on the same circuit that kept blowing the fuse.  Looks like I probably have to replace that sensor ... US$100+ ... waaaah.  I'm such a cheapskate ;-)

 

 

[JONO49 201]

I doubt very much it will be that, but willing to be proven wrong......I'm with the horn or it's wiring loom.

[Slowboy 20,354]

3 hours ago, JONO49 said:

I doubt very much it will be that, but willing to be proven wrong......I'm with the horn or it's wiring loom.

Without seeing it, I’m very much with Jono49. I’d unplug the horn to see if the problem went away first, then get a multimeter on the loom to check it for an earth on the positive side. I’d also check the sensor to see if it’s got very low resistance compared to its specification.

[SteveThackery 3,090]

On 2/14/2021 at 12:38, slowboy said:

Without seeing it, I’m very much with Jono49. I’d unplug the horn to see if the problem went away first, then get a multimeter on the loom to check it for an earth on the positive side. I’d also check the sensor to see if it’s got very low resistance compared to its specification.

 

But in that case the fuse would only blow when you operated the horn, wouldn't it?

[listener 11,158]

8 minutes ago, SteveThackery said:

 

But in that case the fuse would only blow when you operated the horn, wouldn't it?

 

Not if the short is in the horn windings.

[Slowboy 20,354]

1 hour ago, SteveThackery said:

 

But in that case the fuse would only blow when you operated the horn, wouldn't it?

You make a good point. And to think I used to be a diagnostic technician. I will write out 100 times; BUFFS! 😂

[SteveThackery 3,090]

6 hours ago, listener said:

 

Not if the short is in the horn windings.

 

I don't understand.  You mean the windings might be shorted to earth?  So that assumes the horn circuit uses a low-side switch, is that right?  (I haven't got my shop manual any more.)

[listener 11,158]

12 hours ago, SteveThackery said:

 

I don't understand.  You mean the windings might be shorted to earth?  So that assumes the horn circuit uses a low-side switch, is that right?  (I haven't got my shop manual any more.)

 

Okay, I'm being an idiot! 

It's switched live, so not a short across the horn windings then.

 

If the US variant is like the UK one, the Illum/Stop/Horn circuit is fed from fuse 5.

This in turn feeds the rear brake switch and the Junction B terminal block.

The Junction B block feeds the horn, front brake switch, tail light, position light, indicator relay, the VS sensor and the dash instruments.

 

So maybe there's a short in one of the light sockets (tail, position or indicators)?

Or maybe a short to ground from a switch (horn, indicator or brakes) live?

Knackered VS sensor?

A duff dash (maybe just the backlight)?

 

If you feel up to it, it may be worth taking the switch pods apart to check the switches.

Clean off any crud and check for damage (like loose bits) to the switch gear.

 

Edit: By "you" I mean the OP, Gerry. 

Edited February 17, 2021 by listener

[mistergerf 38]

 

Thanks everyone for your input ...

 

It was indeed the speed sensor, it was intermittently shorting the powered side to ground.  Eventually it failed completely.  Installed a new sensor and OEM fuses and all is well.

 

The search was complicated by my using cheepo, non-OEM fuses that just seemed to blow willy nilly.

 

Many thanks to "davebike" for the debugging technique, that's what got me zeroed in.

 

Back burnin' up the miles on the US101 ! ... next stop 200,000 miles ... maybe

 

Edited March 7, 2021 by mistergerf

[wjvh 999]

Well done Gerry, good problem solving. 👍

[Slowboy 20,354]

Good problem solving, and thanks for posting the answer, that will be useful for someone else one day. Nice job.