diagnosing blowing fuse - help?

[Ian Geary]

Evening all

My 2012 street triple is quite low mileage, and mechanically pretty good shape at 16k miles.

Last week noticed the 10amp fuse that powers horn, indicators and brakes was blown.

Replaced it (fiddly, as tank has to come up) but blew again after riding (but not when tested with ignition on?). Gone through 3 fuses in a day.

Bike also flattened battery overnight after I had replaced fuse (this is a new phenomenon..the battery usually holds its change well)

i've done some diagnosis, but am stumped.
I would be grateful if people could check my thinking and give any pointers.

Things I did
- test currant draw by putting dmm in series with the negative terminal. The circuit that blew is drawing 0.4 amps..no other circuit is.
- have disconnected each component from the loom...currant draw remains unchanged (ie eliminating each light or switch etc had no effect)

- visibly checked all switches and connectors. No sign of arcing or water ingress, and from what I can see of the loom it's in good shape

- all the lights and horn work with a new fuse in

- resistance: with ignition off, I put resistance meter between the loom side of the fuse and battery (no continuity) and then operated each item. None of them caused any sudden continuity jump.

Are there any other tests i've missed? Pr have I fluffed up any of the above tests?

It's hard to test electrics with the engine running because the tank has to go back on, and the stupid quick release (haha) hose doesn't really have the slack to move the tank to one side.

I guess power from another live circuit might be getting into the horn/brake/indicator circuit and blowing it?

I've not tested the reg/rectifier yet, which is often a standard answer for bike electrics.

I will get a new battery at some point, but don't see how a worn battery could cause a fuse to blow repeatedly.

I guess I could put a 50amp fuse in and see which bit of the bike gets hot I suppose, but we're a bit early for bonfire night.

Many thanks

Ian

[ruggedscotty]

Had this before, only thing is to take one thing out at a time, complete check of loom, for chaffing bending and any damage. check holders terminals etc for any possible shorts. you can find it quickly or it can take an age to find it.

[Penelope Stopit]

Has an immobiliser or alarm been wired into that fused circuit? 0.4 Amps will drain the battery and there is a good chance that whatever is drawing that current is also intermittently going full short circuit and blowing the fuse

Here is a link to a website that has a diagram and seperate components list (Key), this may well match up to your machine, having looked at the diagram it does show all those circuits you mentioned on the one fuse

You may already have this but.... https://www.freeranging.net/blog/bikes/repairing-t...

[Ian Geary]

Thanks both for your replies. I will look at that link.

No, no alarm. I did wire in an air horn when I got the bike, but it's on a separate fuse.

I did have the airbox off a couple of months ago for a spark plug and thermostat change so perhaps something got routed badly after that.

The currant draw...so is that a bit of positive charge leaking through to ground? Nothing is actually "on" from what I can tell, but for the drain to happen is something actually consuming power?


And to find faults i'd be looking for wiring that doesn't have continuity (though a break would cause an open failure rather than a short) or wiring being live when it shouldn't, which would indicate fraying and shorting between circuits.

Bugger...that's a lot of testing, and for all I know it only does it on full right lock.


Ian

[GreenV8S]

Given the small number of components on that fuse I suggest simply disconnecting the horn and removing the bulbs. If there is still any current drain, there's something else connected on that circuit. If so, I suspect the next job will be tracing the loom carefully to see whether it has been spliced or damaged.

[Penelope Stopit]

Have you looked around the machine in the dark

The rear brake switch wiring could be shorting to the rear light/number plate light wiring and sometimes shorting to earth which will blow the fuse

0.4 Amps battery drain

Watts = Volts x Amps

4.8 Watts = 12 Volts x 0.4 Amps

4.8 Watts could be drawn by an illuminated 5 Watt bulb or semi illuminated 5 Watt bulbs

[Ian Geary]

Penelope Stopit said:

Have you looked around the machine in the dark

The rear brake switch wiring could be shorting to the rear light/number plate light wiring and sometimes shorting to earth which will blow the fuse

0.4 Amps battery drain

Watts = Volts x Amps

4.8 Watts = 12 Volts x 0.4 Amps

4.8 Watts could be drawn by an illuminated 5 Watt bulb or semi illuminated 5 Watt bulbs

Thanks. There's so much info on the internet it's easy (for me) to miss the basics.

[Penelope Stopit]

Good luck in finding it

[PositronicRay]

Whilst it's unlikely to be your problem, never rule out faulty fuses.

I purchased some 16a from a well known national motor accessory shop, they kept blowing. Ordered some elsewhere and all has been fine.

[Penelope Stopit]

There's a permanent 0.4 Amp drain on the battery when the short isn't on the machine

[hellorent]

Try replacing the fuse with a 12v test lamp, then have a wriggle of wiring etc, when the short
occurs the lamp should light you could also use 12v buzzer & when buzzer sounds that should
highlight area of short

[Ian Geary]

Hello again,

Thanks for the encouragement. So I might have made a miscalculation with measuring

With my meter set to 20mA it reads 0.37. So rather than 0.37 amps it's 0.0037 amps.



The thing drawing the current is the digital instrument cluster. When disconnected, the draw drops from 0.37 to 0.02 (again on the 20mA scale)

I'd expect the cluster to have a small draw, which is why understanding the scale of what i'm measuring would be useful!

The instrument cluster gets a feed from the same circuit that keeps blowing a fuse, so it's not inconceivable that I have stumbled on the culprit. (Though I'm still no closer to fixing it)

The dials kept working even after the brake/indicator/horn fuse had blown as I think they also get a feed from the engine ecu.

I will open it up next...the odds of spotting a failure just about outweigh small bits flying in all directions.

[Penelope Stopit]

Ian Geary said:

Hello again,

Thanks for the encouragement. So I might have made a miscalculation with measuring

With my meter set to 20mA it reads 0.37. So rather than 0.37 amps it's 0.0037 amps.



The thing drawing the current is the digital instrument cluster. When disconnected, the draw drops from 0.37 to 0.02 (again on the 20mA scale)

I'd expect the cluster to have a small draw, which is why understanding the scale of what i'm measuring would be useful!

The instrument cluster gets a feed from the same circuit that keeps blowing a fuse, so it's not inconceivable that I have stumbled on the culprit. (Though I'm still no closer to fixing it)

The dials kept working even after the brake/indicator/horn fuse had blown as I think they also get a feed from the engine ecu.

I will open it up next...the odds of spotting a failure just about outweigh small bits flying in all directions.

When viewing the diagram at the above link it can be seen that the instrument cluster has a permanent supply to it at pin 2 from fuse 4

There is also a supply to the instrument cluster at pin 3 from alarm pin 1, this same supply also switches in the Engine Management Relay and Fuel Pump Relay, hence this supply is only live when the Alarm/Immobiliser is deactivated

Delving deeper, it looks like the supply that the Alarm/Immobiliser switches to the instrument cluster pin 3 and the above mentioned Relays originates from fuse 4 which connects to Alarm/Immobiliser pin 6

(Unless we are looking at different diagrams, there is no supply from the engine ECU)

The current draw of 37 Milliamps is a touch high but nothing extreme, 25 to 40 Milliamps is often measured at car batteries

Are you able to ask Triumph what the current draw should be when the machine is parked up

Often it is found that the initial current draw measured does reduce after up to as much as half an hour after switching everything off, it will be worth checking for this

[Penelope Stopit]

ignore the above post regarding the current measurement

That makes 2 of us miscalculating the reading

Meter is set to 20 Milliamps range and reads 0.37 Milliamps = 0.00037 Amps

Nothing to be concerned about, that's a very low current draw and won't drain a good battery for many days

[imagineifyeswill]

Im not really well informed on bikes but due to my job I have had to deal with them occassionally. On any electrical breakdown Ive dealt with on a bike was due to burnt multi plugs or chafed wiring. As it only happens on full right lock I would be looking for a wiring loom around the top yoke/headlamp area getting stretched and chafing or trappped.

[Ian Geary]

Hi there,

Thanks again. It doesn't do it only on full right lock..that was me mumbling to myself.

I decided to stop chasing theories and just re-create the problem.

Put it mostly back together, put ignition on and then turned on indicators and brakes in sequence whilst rocking the handlebars)

With my foot on the rear brake pedal for about 5 seconds there was a rather impressive "ftzz" noise and a distinct puff of smoke that wafted up from the rear brake switch, accompanied by the tink of a fuse blowing.

I'm a bit tired now, but tomorrow I will definitely investigate this again. (I did before, but just jabbed the rear brake on and off which probably didn't re-create the fault)

I would agree chaffed wires are the biggest culprit, but the rear brake switch is also pretty exposed.

Ian

[Penelope Stopit]

Nice find

[Ian Geary]

And to round this off before it sinks into ph anonymity, the cause of failure is the rear switch.

The brake pedal acts on a spring, which pulls a plunger down between 2 copper contacts.

The plunger has a non conductive sheath followed by a conductive part. When pulled down enough, the conductive part bridges the circuit and lights the brake light.

Except, my plunger seems to go too far down, until the top of the plunger is itself touching a contact.





The plunger connects to a spring, hooked on the footrest, which is bolted to the frame, and therefore shorts the brake light signal to earth through the spring.

I'm happy enough with that as an explanation, and can obviously just leave the switch removed until the internet brings me a new one.

Also want to say thanks to Penelope for their ideas and input.

Ian

[Penelope Stopit]

Glad to have possibly been of some help in finding a diagram

Always worthwhile replying to topics that contain in depth information about the problem

That was a very good fault to diagnose

Thanks for posting the outcome

Enjoy

Yamas

[E-bmw]

It could be that someone has changed the spring at some point for a shorter one as the adjustment in the switch barrel should be such that it just makes the contact on braking, and should not be able to go as far as yours does.