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Discussion Starter #1
Can anyone give me any pointers on the 15 Amp fuse to headlights blowing please. Bike is a 2000 F4 750 strada(standard model)
It doesn't blow immediately fitted, and I havn't tried starting the engine then seeing if it blows immediately yet. But it blew another one in the 4 minutes it took me to get to the petrol station.

She has not seen any water in ages, so can't be a damp issue?
The only thing I can say incase related is the fairing etc was off recently when I had my head bearings checked and tightened.
All other Electrics are fine, no issues.

Can I stick in a 20Amp+ fuse, or will that just cause a fire:laughing:

Thanks for any help.
 

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The only other thing that i know of which could be causing such a symptom would be an arc in the wiring somewhere. Chances are its grounding along the harness, or could ground to frame if insulation is breached. Time to pull out the multimeter and have a fit chasing a gremlin. If you get luck hopefully you can find the cause with a little visual inspection of wiring. Look for places it can contact metal, its taut, and check connectors for loose wires or corrosion. All of those can contribute to the blowing fuse.
If somewhere along the harness there appears to be some pinching or crimping carefully dig under insulation wrap on the harness and inspect each wire thoroughly in that area. Sometimes mashed wiring inside the harness can rub the wire insulation thin and allow for arching between wires.....although usually less common than the other things mentioned before.



EDIT: FYI, if a bike sees large temp. swings this is enough for condensation to build up on electrical parts and can be a precursor to corrosion setting in. Even sitting in a garage with lots of rain storms passing will do it too if its not air tight and temp controlled. Granted, these are more the exceptions to the rule, but it does happen. So one can't rule it out.
 

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Discussion Starter #4
Time to pull out the multimeter and have a fit chasing a gremlin.
That bit sounds fun!

Thanks for the input varium, maybe whichever tech I go to might get lucky early?
I didn't really hope it might be simple, but you never no?
I was just hoping for some pointers to pass along.
 

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I wouldn't use a larger fuse, the fuse is rated at 15amp for a reason. Using a larger fuse without finding out and rectifying the reason why it is blowing the lower amp fuse runs the risk of melting wires, blowing your headlight or worse.

Much cheaper in the long run to sort the issue out properly
 

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Paul,

Here is a pic from the wiring diagram for your bike. It is relay 44 low beam.

There is a diode shown on the diagram. Maybe somebody who is bright electronically could qualify this theory, but as I read the diagram, if the diode is blown, current will flow straight to ground and blow the fuse quite nicely ?

Normal operation.

Relay energized via O/Bk to ground B

Switched current then flows from Sb/R through Gr/Bk to Low Beam Bulb ..Bulb lights up

Fault.

If diode is blown, current shorts from O/Bk to B ( Ground ) Fuse B2 Blows 15A


This is only my theory I am not an auto electrician !

Joe
 

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And here is another area you could look at Paul.

light switch at handlebars

Sb/R terminal 1 through to G/R carries feed current via fuse B2

If there is a short to wire B ( GND ) in the switch then you will blow the fuse ?

Good luck !
 

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If the diode is blown, then the path to ground would always exist and the fuse would blow immediately.

I would put in a fuse, start the bike, wait the requisite five minutes and then start fiddling with things.
Take the steering from lock to lock slowly, give the headlight a whack or a wiggle, bounce the suspension...etc. One of these things might show the issue.

What is the last thing done to the bike before the fuse started blowing?

Do not replace the fuse with a higher amperage as this will transfer the load break capability to some other, more expensive, component.
 

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Since the fairing was off, I'd remove it again and check for chafed wiring.
 

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Since the fairing was off, I'd remove it again and check for chafed wiring.
Hi Chuck :)

When you switch on your 750 the parking bulb lights up but not the low beam.? The low beam is only powered up after start up.

This is how it is on my 312 and my 1000R.



Digression.
As a side point....The right side switch gear ie start and kill , on your 750 is wired differently than your 312 so don't swap em. They look the same externally but are different inside.

I snagged this with Brendan ( AgustaBull ) to get his bike running. He had a 750 switch on a 312 harness..

joe
 

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I was just perusing the wiring diagram, yes, they are different. I'll check what happens with the 750 in a moment. Usually, the culprit in a fuse situation is what ever was done last. I found that out when I put new horns on a ZX-11. Every time I made a hard slow speed right turn, the main fuse would blow. I went through 20 of them before someone said....didn't you just replace your horns? I found a place where the horn hot stab would contact the fork and short......:jsm::smoking:
 

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I was just perusing the wiring diagram, yes, they are different. I'll check what happens with the 750 in a moment. Usually, the culprit in a fuse situation is what ever was done last. I found that out when I put new horns on a ZX-11. Every time I made a hard slow speed right turn, the main fuse would blow. I went through 20 of them before someone said....didn't you just replace your horns? I found a place where the horn hot stab would contact the fork and short......:jsm::smoking:
It is very hard to diagnose electrics on the internet Chuck...Your principle of checking last thing done is a good one of course.

The headlight relays sit up on the cheek ( I think left ) of the headlight and so could have been whacked when the fairing was removed.

I don't know much about diodes apart from the obvious. So when they blow is it all or nothing ? or, could there be a fault condition where the voltage slowly results in current flowing the wrong way ?


I had the horn issue ( pardon expression sir :smoking: ) , with my Jota ..

I know wires can shafe through but normally the problem is at the ends of the wires...connections and components and switches.

Anyway,

I hope he finds the problem.

Joe
 

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On the 750, the low beam, or the high beam if selected, come on, in addition to the parking lights, with the ignition switch in ON.

I have the spots before me eyes to prove it!
 

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I don't think diodes can slowly stop providing one-way current flow, I know capacitors can leak and slowly fail. Sometimes there is simply magic in the wires. When the magic escapes, usually in the form of smoke, it's game over.
 

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Discussion Starter #18 (Edited)
What is the last thing done to the bike before the fuse started blowing?
Not sure if your asking me, or merely telling me what to look for, but the top fairing I presume will of being off when the steering head bearings were tightened. As I read in another thread before and this thread, when a problem occurs(which could be related) go backwards to that point when looking for the problem.
Really need to print this stuff off for a tech, although a tech should know his stuff.
I find perspective of others minds helps. I have not met a tech yet who minded me taking along any help I can. I once took my car to my local garage with an intermittent stalling error, I knew that would be a pain to find, and so looked up the error on the net, and went with what was the most informed opinion. This proved to be correct first time, my tech didn't know where to start and it could be several things. So the problem got fixed first time, quite cheaply. It was the crank case sensor. Diagnostic machines don't always work, different errors can throw up different error codes and so the info can be misleading. To many techs these days rely to much on them, and I fear that they don't have quite the craft as those in the old days, but one could also argue this is the problem with modern vehicles and all the ever so reliant sensors and electronics.

Thanks for all the replies chaps. When this gets sorted(hoping not to expensive)I will post the problem and fix to help others, that's after all part of the beauty of these forums!
 

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Yes, Bert...I'd take the front fairing off and look for pinched or chafed wires in the headlight circuit.
 
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