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Blowing a fuse

A while back I put some purple LED around the engine of my 1400 Intruder.  I never had an issue with them until riding back from Colorado in August 2018, I hit a torrential rain storm.  The lights stopped working.  The fuse blew.  Ever since then, the fuse keeps blowing.  I replace it and sometimes it works for a couple hundred miles.  Sometimes only a few miles into town.  I have looked closely at the actual LED wiring and it is all good. 

Is there a common wire or junction that after it gets wet causes a short?  I am not sure where to start looking for the short.  All of the other electrical functions are working properly.  No other fuses blow.  Only the one for the LED's.

Thank you!!!




When the fuse blows, will the bike run? Just the LED won't work? (Easy stuff first - make sure the light is intended for a 12v DC circuit - I assume it is.). I assumed you have an inline fuse on a supply wire which is wired directly from the battery to the LED light. The ground can be hooked up to any chassis ground.

If my assumptions are correct, your problem is likely inside the LED light. Of course, you want to make sure your supply wire does not ground out anywhere, and make sure your inline fuse is wired OK, (assuming that's the type of fuse the LED has). I'll explain why it's likely the LED is the problem, and how to verify it, if you have the knowledge and/or the tools, or want to buy them. If you don't have the tools, or don't want to do the work, you can have a service person do this, or you can read my description below - if you like, you can also skip to the bottom and see why i think your LED light is the problem - but your should at least check the wiring with a meter to verify this. You can also just buy a new light and try it, if they are cheap enough. There is little chance the problem is anything but the LED wiring or light, if you have an inline fuse on the supply line - since DC current only travels in one direction.

The best way to test the light and wiring is with a continuity tester, a volt meter, or multi-meter - testing for continuity, ohms, or (resistance)... Also, when wiring anything, I strongly recommend always using proper wire crimps or ferrules/terminals/plugs designed for this type of installation - and use heat shrink wrap for insulation on any exposed terminals - never just use electrical tape or just twist wires together. Using crimps and heat shrink wrap is safer and much better practice to avoid shorts or other unintentional issues.

Unwire your LED light from the postive battery terminal, and from the chassis ground or negative battery terminal - whichever is used. Test for resistance or continuity between the LED supply wire (disconnected from the battery) and chassis ground or negative battery terminal - do not check to the negative wire on the LED yet (but this wire should also be disconnected from the chassis or negative battery terminal). The ohm meter should show something like OL, representing infinite ohms or open circuit. If you get a low ohm reading, or positive continuity reading, with the wires disconnected, you have bad wiring or a bad light which is shorted to ground - (the light can short through itself to the mounting bolts, or the wiring can be shorted).

Now check resistance from the positive lead wire, and the negative lead wire of the LED light. A good result will be about 30-60 ohms - I'll explain...

Your LED light will have a resistance built in. The manual or manufacturer of the LED should be able to tell you what that value is... If you have an ohm meter, you can test the positive to negative wire of the light (with the LED disconnected from the wiring on the motorcycle). If you can't find the proper ohm (resistance) specification on the LED device, inside the manual, or get it from the manufacturer - you can look up a website and find a "resistance calculator for LED lights". (For this calculation, count the individual LED's in your device and use that number for the number of LED's - This is your expected resistance you should see on your ohm meter readings.) I'm guessing the LED resistance rating will be about 30-80 ohms, depending how many LED's, what type of LED's, and what resistance is in the LED device. If it is lower than the manufacturers rating, say less than 30 ohms, you may have moisture inside the light or a short inside the light. You shouldn't' get a reading of "OL" for open circuit because you said the light still works for a while, and will always start working again after the fuse is replaced.

SO - Basically, when wired back up, and your motorcycle running, your light is drawing too much current, and this means there is likely a short or loss of resistance in the light which makes it draw too much current - moisture can also do this. This can also be verified by watching the amperage to the LED - (bike running, light ON) - using an ammeter, you can test the amps drawn to the LED supply wire. If the amps raise above the fuse rating, the fuse will blow. (The manufacturer or manual should also be able to supply the amperage rating, so you know what is TOO high.)

IF you don't have a meter to check amps, you can see the voltage drop at the supply wire - setup to test volts on the supply wire, and then start the bike and turn on the LED - note the voltage drop when the LED is switched on or when the bike starts... NOTE: the volts may drop slowly since your problem in not happening right away or all the time. Your electric starter will also make the volts drop, but the volts should quickly rise again after the bike starts and the starter disengages. After that, the volts are supposed to remain steady - but I think with a small amount of time, you will see the gradual loss of volts again, or you will see a voltage which looks too low - this indicates the LED is drawing too much current. NOTE: even though you can get an idea of whats going on by measuring volts, it is best to check amps on the LED supply wire, and not volts - many other items run on the battery, and it can confuse the reading. It is possible the voltage drops quickly, by maybe 1 volt or more, but most likely you will see the volts drop fairly gradually until the fuse is blown. As you rev the engine, or drive faster, the stator will produce more current and likely make the voltage drop even slower - which is why your problem seems to not be the same all the time, and is better on longer trips (likely at higher speeds).

So, again, most likely, if your wiring is OK, you will see that the light draws too much current, and this will keep happening until the resistance issue is corrected. My recommendation is buy a new light if the resistance isn't measuring correctly, or fix any wiring issues you find by measuring continuity or resistance of the wiring. You can also get the proper rating and go to the auto parts store, and compare your LED to a new LED if they will let you... they may even have a meter and measure it for you. For a future install, I would recommend taking some extra time to better waterproof the light and the connections with heat shrink wrap and waterproof connectors on the wiring, and silicone or paper gaskets on the LED light wherever you think water might penetrate - and let the sealer dry before applying power to the LED.

ALSO - if the light can be taken apart, you may be able to clean it out with contact cleaner... and if your resistance is good, you can then re-assemble it, being sure to waterproof it like described above. Since it isn't "totally burnt out", and it keeps working with a new fuse, this is another possibility. Best is to replace it, if the wiring checks OK, however. You don't want to keep doing it over, and over.

I really appreciate the time you took to lay all this out. The bike runs great when the fuse blows and everything else electrical is working perfectly. The LED lights worked well for over a year. Until I hit that torrential rain storm. I replaced the LED control module at which time I replaced both the negative and positive wires. It is wired properly.

That said, I guess it could be the actually light strips. They are supposedly completely waterproof. And sometimes, when I replace the fuse, they will work for a time. A few days ago, I rode over 200 miles and they worked well. Then the next day they blew the fuse and it blew again within a few miles of riding.

I'm not sure how I can test the actual LED wiring. It is a wiring harness that plugs into the control box. I'll give the manufacturer a call and see what they have to say.

Thanks again. I am stumped by this. I was hoping there was a something that commonly goes wrong in the Intruder wiring that I could check. But if everything is working properly, it makes sense that it is in the LED wiring.

OLD SCHOOL. Get a plastic water pitcher or even a old plastic milk jug and starting at the farthest point wet down one section at a time. Don't know what you paid for your set up but :

holy cow it wasn't an essay question

Well, if your wanting to get technical. Electric current in a wire moves at 0.7c to about 0.9c., c being the speed of light. If you consider the effect of a short to be equal to closing a switch, then then the leading edge of the propagating wave moving away from the short i.e. switch is close to instantaneous.
Vibration, heat expansion and moisture can all create a temporary path to ground and. there goes the fuse.
One of my instructors who had been in R&D at Suzuki referred to this intermittent condition as a "swinging short".

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