Blowing 20 amp main fuse

The tail light runs directly off the key switch on the '78 and later models. '77 and earlier models power and control it through the headlight on-off switch on the handlebar. And as it should be I might add, lol.
 
XSLeo said:
With the screws missing/loose the contacts open and close quickly. This may cause power surges that may be enough to blow the fuse.
Often a short in the tail light can blow the main fuse. It runs directly off the key switch.
I like the way the early switches had screws, easy to take apart and clean.
Leo
Click to expand...
Jim said:
It's possible one of the coils is getting hot and shorting out. Can't really think of a good way to test fort that. :umm:
One thing you could try is adding a 10A in-line fuse to power in, on each coil... either temporarily or permanently. If one blows you'll know it's that coil. If the 20A still blows, at least you'll know the problem is elsewhere.
Click to expand...


Hey Jim, let me ask you a question. (obviously the ignition wiring didn't solve my problem), if only one coil is bad, shouldn't the other cylinder still fire?
 
Shipper said:
Hey Jim, let me ask you a question. (obviously the ignition wiring didn't solve my problem), if only one coil is bad, shouldn't the other cylinder still fire?
Click to expand...
It would if it still had power, but the 20A fuse blowing kills ALL power to the bike. With 2 separate 10A fuses... yes, if a coil blows one fuse, the other cylinder will continue to run.
 
Gentlemen it sounds as the problem is still there cant remember if I pushed this.
But for 35 Years virtually all problems with my bikes was / Is in the charging circuit.
Some minor with ignition including kill switch and even less problems with the Carburetor .

A first check of charging Voltage at little Higher rev so it is not to high
And then if the method of adding Fuses is selected --- May i Suggest that one is installed in the charging circuit. Directly. When the tools are out.
Ignition is new + the same Coil as did not burn the fuses before.
I am not saying that a fuse there is not something to try .But as I Se it , it can be elsewhere.
And on my bikes as a rule of thumb always in charging.
 
Thanks Jan, am going to check the coils with fuses then the charging system is next. Kinda think coils ain’t the problem as you say they weren’t a problem before points replaced but it’s where I will start next. The weird think is that once the 20 amp blows I can replace it immediately and it will run fine to get me home?!?
 
Shipper said:
Thanks Jan, am going to check the coils with fuses then the charging system is next. Kinda think coils ain’t the problem as you say they weren’t a problem before points replaced but it’s where I will start next. The weird think is that once the 20 amp blows I can replace it immediately and it will run fine to get me home?!?
Click to expand...


I guess the question becomes - what could possibly cool off that fast to allow perfect running minutes or seconds later? Sure sounding more like a wire short but I’m sticking with my plan. Coil/charging/whole wiring harness. Getting thoroughly stressed but can’t believe how well it starts and runs prior to fuse fail.
 
Shipper said:
Thanks Jan, am going to check the coils with fuses then the charging system is next. Kinda think coils ain’t the problem as you say they weren’t a problem before points replaced but it’s where I will start next. The weird think is that once the 20 amp blows I can replace it immediately and it will run fine to get me home?!?
Click to expand...

My idea in that respect as mentioned ..when used an electrical circuit gets warmer
Heat is generated thermal expansion in circuit so does the metal it also changes. Form and shape
So fex copper wires in an alternator might move around due to the generated heat.
When the heat goes away ..due to the Blown Fuse .the heat input disappears.
In some cases that rather quick changes things.
If I get the Math right a Coil with ca 4 Ohms Resistance
Has with 12 V U=R x I ---> 3 Ampere
Electrical power P=U x I 36 Watt .. Not that little.
Adding to that that --- vibrations can be a factor
That also goes away when things stall.
If it is a loose badly clamped wire that shorts the vehicles position can be a factor.
fex Sharp left turn the wire moves shorting out.
Stop and the bike is upright the cable can be in another position .New fuse
And at the next turn same again.

I cannot say where it is But the Charging circuit is the part where I have had most Problems.
2 or 3 rotors 2 or 3 stators . 2 or 3 rectifiers .
4 -5 regulators.
If you have the stock mechanical regulator .Do check output voltage.
Those have a bad reputation and I have had one giving over 15 V.
If no voltmeter on the bike you don't notice it easily.
On a positive note you come home ..that has not always been the case for me.
It is vintage bikes some problem will always be there.For most people.

Does the bike misfire or show any other signs before the fuse burns
Lights blinks or so.
Will it burn on a slow run. Holding longer time with low rev ? Runs ??
 
Shipper said:
Only burned once on a slow run. 3 times now on high load. Given me a lot of homework and additional things to learn and consider.
Click to expand...

Have not heard if you own a Voltmeter -- If not -- those are not expensive 10 --15 $ US .For a usable one
From an automotive Shop . Then I / We can ask you for readings on that one and it is easier to give suggestions on line.
It need resistance capability and a 20 V measurement range .capability
Or you can borrow one .Or take the bike to a service station were they can measure.
But in my opinion a Voltmeter is a thing to have when into these bikes.
The first thing would be to measure voltage across battery at idle and on ca 2- 3000 rpm.
I would check slip ring resistance on the Rotor also . you can find how to do that here on line
It might not show any faults cold but I would still try to measure it.
Those have a low resistance between slip rings. When working and can have even less if faulty.
It might short there.
If that is low an additional fuse in the Charging circuit would be again a thing to consider.

Please give info of what bike Year and type so I / We can find the right schematic on line

"The moving cable " is something virtually impossible to find since nothing manifests when the cable is in the " Right Position "

Having said that I cant remember really in 35 years a single stripped wire shorting .On My two bikes.
It is in 95 -98 % of cases in a Connector or in a Component as the regulator alternator ignition lock
Fuse box Kill Switch and rectifier and so on

Are there any extra non stock electric accessories or components on the bike., or has been.
 
There is a "thing" on XS650s
The grommets at the back of the headlight bucket rot and the metal bucket edge is exposed. It cuts into a wire bundle causing intermittent shorts.
 
Jan_P said:
Have not heard if you own a Voltmeter -- If not -- those are not expensive 10 --15 $ US .For a usable one
From an automotive Shop . Then I / We can ask you for readings on that one and it is easier to give suggestions on line.
It need resistance capability and a 20 V measurement range .capability
Or you can borrow one .Or take the bike to a service station were they can measure.
But in my opinion a Voltmeter is a thing to have when into these bikes.
The first thing would be to measure voltage across battery at idle and on ca 2- 3000 rpm.
I would check slip ring resistance on the Rotor also . you can find how to do that here on line
It might not show any faults cold but I would still try to measure it.
Those have a low resistance between slip rings. When working and can have even less if faulty.
It might short there.
If that is low an additional fuse in the Charging circuit would be again a thing to consider.

Please give info of what bike Year and type so I / We can find the right schematic on line

"The moving cable " is something virtually impossible to find since nothing manifests when the cable is in the " Right Position "

Having said that I cant remember really in 35 years a single stripped wire shorting .On My two bikes.
It is in 95 -98 % of cases in a Connector or in a Component as the regulator alternator ignition lock
Fuse box Kill Switch and rectifier and so on

Are there any extra non stock electric accessories or components on the bike., or has been.
Click to expand...

Jan, will follow your suggestions. Really hard to believe it’s a coil based on characteristics of fault (starting right up and running with a new fuse). The bike is a 1975 650xsB.

Thanks
 
Jan_P said:
Have not heard if you own a Voltmeter -- If not -- those are not expensive 10 --15 $ US .For a usable one
From an automotive Shop . Then I / We can ask you for readings on that one and it is easier to give suggestions on line.
It need resistance capability and a 20 V measurement range .capability
Or you can borrow one .Or take the bike to a service station were they can measure.
But in my opinion a Voltmeter is a thing to have when into these bikes.
The first thing would be to measure voltage across battery at idle and on ca 2- 3000 rpm.
I would check slip ring resistance on the Rotor also . you can find how to do that here on line
It might not show any faults cold but I would still try to measure it.
Those have a low resistance between slip rings. When working and can have even less if faulty.
It might short there.
If that is low an additional fuse in the Charging circuit would be again a thing to consider.

Battery charging at 13.58v

Please give info of what bike Year and type so I / We can find the right schematic on line

"The moving cable " is something virtually impossible to find since nothing manifests when the cable is in the " Right Position "

Having said that I cant remember really in 35 years a single stripped wire shorting .On My two bikes.
It is in 95 -98 % of cases in a Connector or in a Component as the regulator alternator ignition lock
Fuse box Kill Switch and rectifier and so on

Are there any extra non stock electric accessories or components on the bike., or has been.
Click to expand...
 
Hate to even suggest this, but roughly above the carbs in the main harness Yamaha used a couple of crimps to connect grounds. With age they can start to heat cause insulation on nearby wires to melt, you get the idea. can also happen at harness kinks, think up near the front of the gas tank.
 
Jan_P said:
My idea in that respect as mentioned ..when used an electrical circuit gets warmer
Heat is generated thermal expansion in circuit so does the metal it also changes. Form and shape
So fex copper wires in an alternator might move around due to the generated heat.
When the heat goes away ..due to the Blown Fuse .the heat input disappears.
In some cases that rather quick changes things.
If I get the Math right a Coil with ca 4 Ohms Resistance
Has with 12 V U=R x I ---> 3 Ampere
Electrical power P=U x I 36 Watt .. Not that little.
Adding to that that --- vibrations can be a factor
That also goes away when things stall.
If it is a loose badly clamped wire that shorts the vehicles position can be a factor.
fex Sharp left turn the wire moves shorting out.
Stop and the bike is upright the cable can be in another position .New fuse
And at the next turn same again.

I cannot say where it is But the Charging circuit is the part where I have had most Problems.

Battery charging at 13.58v
2 or 3 rotors 2 or 3 stators . 2 or 3 rectifiers .
4 -5 regulators.
If you have the stock mechanical regulator .Do check output voltage.
Those have a bad reputation and I have had one giving over 15 V.
If no voltmeter on the bike you don't notice it easily.
On a positive note you come home ..that has not always been the case for me.
It is vintage bikes some problem will always be there.For most people.

Does the bike misfire or show any other signs before the fuse burns
Lights blinks or so.
Will it burn on a slow run. Holding longer time with low rev ? Runs ??
Click to expand...
 
Did you pull the left engine side cover off and inspect the harness as it comes out of the alternator? Routed wrong this can get cut and shorted by a loose chain.
 
gggGary said:
Hate to even suggest this, but roughly above the carbs in the main harness Yamaha used a couple of crimps to connect grounds. With age they can start to heat cause insulation on nearby wires to melt, you get the idea. can also happen at harness kinks, think up near the front of the gas tank.
Click to expand...

Thanks G’s, looks like I’m ripping wire harness tape next.harness
 

Similar threads

bosco659
Blowing fuse?
2
Replies
29
Views
1K
bosco659
bosco659
H
has compression, spark, and fuel but won't fire / start - cam chain issue?
2
Replies
36
Views
1K
Jan_P
J
Hardfahrer
Main fuse blowing...Sometimes. Need Advice.
Replies
9
Views
1K
XSAndy
XSAndy
C
Electrical gremlins - blown main fuse, melted connectors, bad neutral switch, and dead turn signal
Replies
6
Views
497
5twins
5twins
Link94
Blowing main fuse
2
Replies
26
Views
3K
Link94
Link94
Back
Top