Bandit 1200 popping fuses

[Tierbirdy]

2001 Bandit 1200S. Im looking for a second (or more) opinion:

It pops the same fuse every time, the 15A auxiliary fuse (the one that controls rear lights, indicators, horn and the clocks). There seems to be no particular reason or cause for this, initially I thought it was potentially a short in the wiring after I installed new LED indicators, as it started happening about a week or so after doing that. But having checked and re-checked the indicator wiring theyre all fine. Changed the fuse and it lasted a few days. Then I thought it might be a problem with the regrec over-charging as I noticed it did it during a particularly hard overtake. Changed the fuse again and this time it lasted about 10 minutes and popped it whilst coasting to a stop at a roundabout.

Over a similar-ish period of time Ive also been having issues with the battery not holding charge and being flat in the mornings, again no particular pattern to this, some mornings it does, bump start it then itll be fine for a few days, then its flat again

The only test Ive done so far due to lack of any further ideas, is putting a multimeter across the battery terminals, which gives me the following readings:

Ignition off - 12.4V
Ignition on, engine at idle - fluctuates anything from 14.8-16.5V
Ignition on, revving the engine to about 5k RPM - around 15V

That all seems fairly normal-ish, internet seems to imply Bandits can tolerate up to 16V but that its unusual to be getting that voltage at idle.

Heres where it gets a little odd,

Ignition on, holding the throttle open just a tiny bit, around 2k RPM so slow manoeuvring/pulling away speeds - it drops to 5-7v and will stay there for a while then at idle or acceleration it bounces anywhere from 10-16.5V

Mate has suggested this implies either the alternator or the regrec is fucked, as the regrec on the bandit is inside the alternator theyre practically one unit. Its also about £300 for a new regrec or £60 for a 2nd hand alternator & regrec unit off eBay. However before I spend £60 on what may be the problem, and the absolute ballache it looks to be to change the alternator... is there anything else I should consider checking? The battery voltages fluctuating all over the place, and the battery not charging properly sometimes makes me think it may well be a problem with the alternator but then if its a voltage problem with the alternator/regrec, then why is it popping the same fuse every time? And why the 15A one rather than the lower 10A ones, or headlight bulbs? (everything except the main/dipped beam has been replaced with LED).

[Pete.]

No reason why over-charging should be blowing the aux fuse.

Did you do any soldering when you fit the LED's? If you did, go over the joints looking out for spiky bits that might short on something. I had a bike with a gash alarm installation that had a solder spike that poked out through the tape they used and shorted on the frame.

As for the random voltages, un-plug the reg rec from the loom and inspect the terminals.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Tierbirdy]

I can’t unplug the regrec as it’s buried inside the alternator as three seperate parts

As for the indicators, no soldering. The previous owner has done an utterly shit job of wiring in his own aftermarket bulb indicators, he’s cut and spliced the wires into each other by just twisting them together and covering in tape. I cut that shit out and crimped on some spade connectors and heatshrink & taped over them individually so there shouldn’t be any way they can short out. Gave them a look over yesterday and they look fine. I’m concerned what other shit bodge jobs he’s done...

[Islander]

[MCN]

If it's not a consumer in aux going rogue and pulling too much current then it can only be part of the aux circuit touching ground.

If it only blows whilst running or moving that suggests a loose cable (or something) touching ground.

If you have the specs for the consumers you could put an ammeter in-line to each one and see how much currrent they draw.

Probably a first check would be to check resistance in the aux circuit and components one-by-one.

But you are correct in assuming that you have an electrical problem.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[Suntan Sid]

Had a similar problem a few ears ago, although I was blowing bulbs not fuses.
Everything checked out fine with a meter and visually, the problem in the end turned out to be the bulb holder itself. One of the metal tabs, (which the wire was soldered to), had cracked.
When I fitted a new bulb it would work fine, once I fitted the lens back on it would work for a couple of seconds then blow the bulb.
The act of screwing the lens back on was enough to deform the unit slightly and move the cracked tab slightly.
A blob of solder fixed the problem!
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"Everybody needs money, that's why they call it money!"

[stinkwheel]

Plug a bulb and holder with two flying leads and some spade terminals in where the fuse goes (in place of it). When the short happens, the bulb will light up brightly instead of blowing the fuse.

You can then tell when you've wiggled the correct wire. I bet it lights up at 2,000rpm. Checkthe usual places on the wiring. Anywhere it passes through or under a plastic, under the saddle, around the headstock.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[mudcow007]

My Bandit kept popping the 30A fuse totally randomly - would sometimes last for weeks without popping

Finally figured out it was a bit of rough metal from where the tank is fixed to the bike at the back of the tank rubbing into the loom

[MCN]

If you don't have a 'tracer' device

Vehemo Automotive Short Open Finder Cable Circuit Car Wire Tracker Detector Repair Tester Tool
https://s.aliexpress.com/BziIBJv2
(from AliExpress Android)

to determine where in a conductor the short is then work by halves.
Find the mid-point (Or as near as you can get to it) in the wire and meter it.
If it shows a fault then find the mid-point of that faulty section and so on until you narrow it down to the bad section.
Fix the bad bit.
Close the thread. 😆
👍
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.