Blowing 30A fuse - When Hot or Not?

[Rays]

This is a photo of the Uly main diagram from the 2009 Electrical Diagnostic manual - not sure if it there are any major differences to the earlier systems in the main fuse area but these diagrams are colour coded so possibly easier to follow if you aren't into electrical diagrams.

One thing that you do need to check is the voltage regulator and the wiring going to it - it is connected directly to the 30A fuse and has quite a long loom on the 2008+ bikes. I have not personally seen one fail with this symptom but they do have a number of electronic components internally so might be capable of having some sort of intermittent fail.
The other thing you should check is that all the other fuses are the correct rating just in case a previous incorrect replacement has left you a little landmine that is masking the problem. Very unlikely but if you aren't the original owner then you never know.

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[Barrett]

Steve: Ray made an excellent observation and suggestion above and I should have recalled that scenario from a few years ago. The 03-07 VR made its connections behind the front pulley cover....the 08-10 VR connects behind factory left front air intake scoop. The only blown 30A fuse...which is the battery fuse...that I ever had to deal with in all these years, was due to a failed VR on a 2008 XB12 I had purchased. My apologies for not recalling that. I tested it as follows:
1-Replaced 30A fuse...started and throttled up motor with volt meter attached to battery terminals. As soon as the voltage would spike to above 15 DC volts...the fuse would pop.
Test yours.

[Pushr0d]

Guys, thanks again for the posts and advice!

I put a MOSFET VR on the bike a long while ago. I have a USB adaptor in my front 'accessory socket' that includes a voltmeter, which I can see if it isn't in direct sunlight. I've never seen it go above 14.4V, but I'll try the throttle test. I'll certainly examine the left side cabling, though! I've had a couple 'adventures' with that spaghetti, lemme tell ya!

The weird thing (aren't they all?) is that the failure is so intermittent, with no apparent common condition. And, it's happened five times in two years. The only thing that might be significant is that it seems to happen when the engine is hot/heat soaked. I don't recall it ever happening when cold, or on short trips.

I'll keep you posted!

[34nineteen]

The 03-07 VR made its connections behind the front pulley cover....the 08-10 VR connects behind factory left front air intake scoop.

Good call on that one. I wonder why my wiring diagram didnt show it. I probably needed to look more in the service book. The earlier setup used to have some issues with the connector, but i would also check the wiring from the VR to that connector as well, as it runs directly above the exhaust for awhile.

If the fuse is melting, the issue is likely caused by heat degrading something. When that is the case, the load on the wiring and fuse goes up slowly and everything gets hotter. Normally that will show itself on the fuse as melting. Thats why you see connectors melting and burning as well. Its the constant long term high heat exposure. This can also be caused by poor electrical connectors or poor grounds.

When its a dead short the fuse just pops. It will pop so quickly it really doesnt give the plastic time to melt.

Its a very helpful symptom to know when diagnosing an electrical issue. As you can see in the pic below, even though the fuse hasnt blown, the plastic melted. While the fuse still technically works, its screaming at you that there is another problem at hand. If the plastic on the fuse melted like that, the insulation on the rest of the wiring is probably getting the same heat and abuse, and will could start a fire.

[Pushr0d]

(I'm pretty sure - time will tell.)

So I dove into the bike yesterday morning. Started at the fuse box - pulled it, took off the 'undercover' and gave it a close inspection for loose or corroded connections. Clean and tight. Tried the wiggle test. Nothing. Just for grins, I swapped the Ignition relay for the Auxiliary relay. That's to remove a faulty relay from the issue.

Close inspection of the wiring harness from the fuse box to where it dives into the frame. No apparent damage or even contact anywhere.

Then I removed the left side scoop, and disconnected the cable hangers from it. Now, I had re-done all that when I installed the new stator and the new MOSFET VR. I had extra cabling, as I didn't want to cut the bike side of the harness, so I had an 'adapter cable' that had to stow under there. I cut all of that free, and disconnected the power cable from the VR and pulled it all out so I could inspect it.

I disconnected the 77 plug and the new plug and inspected them, then re-connected them. Then I worked forward.

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Cue Eric at South Main Auto, "There's your problem, Lady!"

At least two points of contact. I put the harness back in place and looked closer to figure out where the cable was rubbing. Apparently it was pressed up against the upper scoop bolt boss when the scoop is installed. That boss is rather sharp. The two 'penetrations' on the wire are about the same distance apart at the diameter of that boss.

I 'patched' the wire with several turns of Tesa tape, and then used a lot of Tesa tape to wrap the entire section. Then I fashioned a couple of pieces of tough foam - one piece fits around the boss, the other over it. All contact cemented together. The foam covers the sharp edges.

As I started this post - it's fixed, I think. I had five fuses pop in two years, so hopefully removing an obvious cause will cure it.

[34nineteen]

Nailed it! Great work!

[Rays]

Nice work - I'm with Eric O looking at that.

[Pushr0d]

So, what have we learned here? The 30A fuse pops. Why?

Barrett gave me a hint, and when I looked carefully at the wiring diagram, it shows that the only component on the red wire from the 30A fuse is the Voltage Regulator. All the other 'taps' have their own 10A or 15A fuse. None of them ever popped.

Assuming the VR isn't failing and spiking the voltage, the only condition that can pop the 30A fuse is a short or connection problem on that red wire.

NOTE: If you look at the schematic in color, you will see that the Red wire from the 30A fuse changes to Black when it gets to the harness connection for the Voltage Regulator. That is not an error. The stock VR has two black leads.

[Cooter]

BTW, they are the same color because they are completely interchangeable. The VR doesn't care what the input order is.

[Tbone]

Wow, this is more motivation to relocate VR. I ride some pretty bad roads. Thanks for posting this and glad you were able to resolve it quickly. Hopefully show how resilient the FH020AA is, or is not?