Why is my bike blowing its main fuse

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SeattleUnderliner

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Hey xs'ers.

Ugh. So my PO changed half of the fuses (main and headlight) to the blade type, and left the other two in the stock fuse box. I have been loosing my battery charge every few days, and have to charge it. Btw, my battery is good. I was in the middle of checking some of my charging system parts when i noticed my main fuse was/is blown. I went to my auto parts store and got new fuses and two more blade style fuse holders i plan to wire in.

Here is my problem and question:

I go to put my new fuse for the main in, and blap, it sparked and blew the fuse. So i disconect the battery, try again, plug in the battery, and blap....blown. I have a 25 bladed fuse in the grage, figure ill try one up, and see if that works. nope. blows that too.

Why is my main fuse blowing? Why will my battery not stay charged?

You may want to know that i am not running gauges or the electronics for them, or turn signals. I can't think of anything else that i removed. Would removing my turn sig make my main fuse blow? i did notice a little hissing today as i charged the battery from this little electric box on the Rt side of the battery box. not sure what it is. it has 3 yellow wires, 1 black, 1 red.

Please help. It was at least running yesterday. I seriously did not do anything today besides try and start the bike, notice no lights, assume my battery is dead again, and decide to start looking into my charging/electrical issues, which is when i found my blown fuse.

ugh. :wtf::banghead: 1979 special BTW. Thanks
 
So believe it or not, my wife is telling me that by removing my turn signals and gauges, i have lowered the resistance and therefor i am blowing fuses. (she is a smart lady!!)

does that make sense? How do i fix this? i plan on running rear turns, but have not got them in the mail yet.

super bummer. Its the perfect weather here in seattle for a nice ride.
 
That would only apply if they were in series. I am not denying that she is a smart lady, but she's wrong. =)

I am going to suggest that when you removed lights from the system you shorted something or left a +V connector loose and it's found a ground. Seems like a sort of obvious thing to say, but there it is.
 
interesting....i did leave all the connector boxes sitting inside the headlight. It did rain a bit, and now come to think of it..... every time there is moisture my battery totally dies. I will go look for a short somewhere. good call.

Also? what would happen if i run a fuse that is to big. like running a 20 for the headlight instead of the 15 it calls for? would it make my light brighter, or just burn it out faster?

sorry. electronics are not my strong-suit.
 
You definitely have a short to ground somewhere. Don't go ramping up the fuse sizes either, you'll burn up the harness.

The fuses are designed to be lighter load than the wiring, if you exceed the wiring capacity with a larger fuse size the wiring fails first instead of the fuse.

Had a guy do that with a brand new charger, put a 30amp fuse in a 15amp circuit because it kept blowing, he didn't realize there was a short in the system, I had to put an entire new body wiring harness in the car!
 
ok. good news and bad news.

I wired in the other 2 blade fuse type holders. I also looked around and tested a bunch of wires and could not find a ground/shorted out wire. also, hard to do when i cant get power to go past my fuse without blowing.

also. if i unplug that little box on the Rt side of the battery, my fuse does not blow. the min i plug that sucker back in, blap, blown main fuse.

what is that thing? and how do i replace it, or better yet, how do i know that it is f*ed up? it is all corroded and beat up.

also. im thinking of doing the banchee mod, should i just jump right into that, or should i try to fix this issue first? im looking for the fastest way to get back running. i was not planning to do the banchee mod till this winter, when i plan to do a full tare-down/rebuild.
 
Attached pic.

1: holding box
2: pointing to where po had attached it.

is it the regulator?
 

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That's your rectifier and they do sometimes go bad. We swap em out for auto rectifiers, or sometimes other heavier duty one-piece units when we happen upon 'em.
 
so. just so i understand what is happening.

my rectifier changes the AC current from my charging system into DC and recharges the battery. It also only lets a set amount of current to flow through the wireing harness.
So....if my rectifier is bad, my battery would loose charge quickly, and i would start blowing fuses? could i really have solved both my problems with one part?

if so....GREAT!!

If i replace the unit, i should not blow fuses right? and my battery should hold/charge better right?

Now, do i get one off ebay, or is there a better replacement part i should get?
 
Last edited:
The rectifier turns an AC voltage into a (pulsing) dc voltage. The regulator tries to keep that from getting > 14.4 ish volts.

We don't know that it is your rectumfrier. Disconnecting that also disconnects ALL of your stator coils as well as opening the charging circuit... so, that's inconclusive.

It's not hard to test the rectumfrier, but you need a voltmeter. True that diodes CAN leak at higher voltages etc. but usually they are open (or shorted) if they fail.

I have a mantra - that is to test, observe and isolate.

Your electrical system is really 4 more or less separate systems.
Ignition output, ignition input, charge, accessories.

If you have a short from batt + to ground, there is your test and observation, now isolate it. Follow that short until you find it.
 
Before you do anything else, check your alternator rotor as per the manual, i.e. check resistance between the slip rings. As a rotor goes bad, the resistance approaches zero, which equals a direct short to ground, which will instantly blow your main fuse.
 
hmm. ok. so what you are telling me is that i may not have found the problem. by disconnecting the rectifier i also disconnected all my stator coils. so how do i locate the problem? with it unplugged, my lights work, and my fuse does not blow. with it plugged in my fuse blows, meaning no power to anything = cant check circuits/wires for a short.

what all do i disconnect when i unplug the rectifier? just the rectifier and regulator i thought. anything else? would getting a combined rectifier/regulator unit be a good idea at this point?

My rectifier is all corroded and bent/messed up.

i will check my alternator rotor also.
 
Always start from the beginning. Assume nothing.

Test, observe, isolate and identify.

You can test for a short without power, in fact you have to. Test for resistance to ground. If it's somewhere near zero ohms, it's shorted.
 
sgallaty: thanks for the help, but honestly.....your mantra means nothing to someone who is trying to still find what and how to test.

maybe your mantra could include some room for a beginner to learn as much as possible.
How do i test (your first step), and WHAT do i test.
 
SeattleUnderliner;

Its quite simple to test the rectifier. There are 5 wires, 3 whites, a red and a black.

Use your ohmmeter on the lowest scale. Connect one meter lead to the red and then touch each of the 3 white. All 3 will read about 7 ohms or they will read high resistance (open circuit) Reverse the meter leads i.e. change the meter lead you have on the red. You now have the opposite condition from the first test, and again will get about 7 ohms or open circuit.

Do the same tests as above except put the meter lead on the black wire.

If your rectifier is bad, you will likely find one of the 6 tests you just did to be different than listed. One of the 6 tests will show low resistance both ways, perhaps one will show 0 resistance..................that's the short circuit.

The best and cheapest thing to do, is make up your own rectifier, your regulator is likely working OK.:

http://xs650temp.proboards.com/index.cgi?board=Charging&action=display&thread=3473
 
The forum has a good Tech section, with wiring diagrams and trouble shooting threads, plus a lot of answers can be found through the search function. Type in Curly in the search. If you don't a Clymer or Haynes manual it would be a worthwhile investment.
 
SeattleUnderliner said:
sgallaty: thanks for the help, but honestly.....your mantra means nothing to someone who is trying to still find what and how to test.

maybe your mantra could include some room for a beginner to learn as much as possible.
How do i test (your first step), and WHAT do i test.
Click to expand...

I am always willing to explain why, sometimes willing to explain what, but you have to learn how on your own. Fortunately there are plenty of sources for this material.
 
Thanks again for all the help.

Looks like its time to buy a few more tools. Believe it or not, my rectifier that was all banged up, bent and blowing fuses, i cleaned up a bit and tried one more time.....ta-da....no blown fuse, and my bike runs again.

still not totally convinced i dont have a short somewhere, and still not sure if my charging system is not working or if my battery is bad. Time to "Test, observe, isolate and identify."

cheers.
 

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