UK Monster Owners Club Forum » .: Technical :. » Electrics » What could be melting my main switch fuse

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Old 21-01-2020, 01:25 PM   #16
Darren69
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I've just had a quick look at the wiring schematic for my S4 which will be similar to the 620. That 30A fuse is called the General fuse but its fed directly from the battery + on one side and the ignition relay on the other side, so check the igintion relay is all good. Its also fed by the reg rec which is behind the 40A main fuse so check the charging is within the limits Gazza said, it could be overcharging. It dioes't look like there is much else on a direct feed from that fuse (The ignition key switch itself.) Those would be the things I would check all connections on first.
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Old 21-01-2020, 04:33 PM   #17
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If you could get your hands on a DC ammeter, pref a clamp meter you could very quickly narrow it down to the specific circuit causing the over-current.
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Old 21-01-2020, 06:35 PM   #18
Darren69
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From what he says the fuse isn't blowing so its not over current. It points to a connection issue causing heat build up over time at which point the heat melts the plastic fuse holder and the resistance is so high that not enough voltage can flow.

I just did a quick google and this article illustrates what I think is the problem:-

https://www.redarc.com.au/faq-tech-t...d-fuse-holders
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Old 21-01-2020, 09:46 PM   #19
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I reckon you’re right there Darren- I see this kind of thing quite frequently in my work where cable connections are not done up properly and heat generated by the current is enough to melt the insulation.

It has been mentioned many times on here where the crimp terminals in the block connectors have either a build up of corrosion or a loose connection leading to high resistance generating heat so the wire and or the connector block itself melts- this is particularly prone to happen on the alternator and regulator/rectifier wires.

Going on from this the under seat fuse holders are basically a series of uninsulated 1/4” faston crimps held in place by the box they sit in. The underside of this fuse box is open to the elements and sits in just the right place to get a bit of spray and road crap from the back wheel leading to, if not cleaned up regularly (yep you guessed it) a higher than wanted resistance.



So as many here have said before me, and certainly as our bikes get older it is definitely worth making the cleaning and applying of some silicone grease to the electrical connections part of your yearly maintenance, especially if you often ride in poor weather.

In addition, the fuse blades themselves will also dull up and corrode over time so either give them a good clean or for the few pence they cost replace them for some new tight fitting ones.

You can even be a bit flash and get some ‘blow glows’- it’s almost worth having one fail just to see it work

https://rover.ebay.com/rover/0/0/0?m...2F291052958453



Personally, as well as the spare fuses that are housed in the fuse box, I also carry (in the under seat tool box) a spare 30 Amp Maxi Fuse (the under the tank one), a new General (Yellow) relay and a puncture repair kit because any one of those can be a show stopper leading to a long wait for a recovery truck.
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Old 26-01-2020, 07:58 PM   #20
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Thanks all much appreciated all the advice. Fuel filter has arrived so I’ll get about changing that and checking all the stuff you’ve highlighted. The 30a fuse in the box doesn’t fit that well, which I put down to the terminal getting hot and expanding. So the fuse is slightly loose in the slot.
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Old 26-01-2020, 08:09 PM   #21
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You might have found your problem.
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Old 30-05-2020, 03:54 PM   #22
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guys, thanks again for your help. by process of elimination, i've been through the r/r, battery, spark plugs, relays and loom checks. Several of you were bang on with the suggestion that gummed up fuel filter was causing pump to draw too much current and burn out the 30A fuse.

That's now all rectified -thanks.

Although I still have the intermittent misfire left over to fix. It's more of a stutter when hot. Should I look next at replacing plug leads, connector etc? Seems a lot of online noise with people having the same or similar issues. Infrequent 'misfire/stutter' in one cylinder when the engine is hot.

Mine normally runs at no more than 119 degrees. which is hot enough to cause resistance in dodgy nearby electrics.

Any classic hot spots?

Cheers
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Old 30-05-2020, 04:49 PM   #23
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Check the state of the big plug on the yellow wires going to the reg/rec, any corrosion in there can cause high resistance.

Front HT lead/cap is in the firing line for all kinds of crap off the front wheel.
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Old 30-05-2020, 05:06 PM   #24
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Quote:
Originally Posted by Skeldy View Post
Several of you were bang on with the suggestion that gummed up fuel filter was causing pump to draw too much current and burn out the 30A fuse.

That's now all rectified -thanks.

My 916 actually melted the fuel pump fuse holder with the fuse in it - it didn't even blow the fuse but the whole thing was a big snotball of melted plastic.

As per yours, blocked filter causing high load and not helped by the usual Ducati marginal wiring...
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