1976 XS650 keeps blowing main fuse

Pina

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Hi Everyone, this is my first post! New to me bike and my first XS650 keeps blowing the main fuse.

Bike has not been ran consistently in about a year the PO said that it sometimes would blow the main fuse. I got it home and went through it and finally got the point to try and get it running.

The first couple of times it started then died. About the 3rd try as soon as I hit the start button the fuse blew. I installed a new one, it cranked, idled for about 30 seconds and the fuse blew. this happened two more times. The last time it blew it happened as I turned the key into the on position. I'm not sure where to go from here. The cables in the start switch were frayed I'm waiting on a new one a new assembly to arrive, I'm hoping that was the cause. There is a cable on the right hand side, near the main fuse, that appeared to be cut and I cant for the life of me figure out what it should be connected to. see attached picture. I looked at a wiring diagram and I think its comes from to the main switch L position but I cant see where its supposed to connect. Its a blue cable with a red stripe.

Can anyone tell me what attaches here?
 

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A fuse is in the wiring in-case there is a problem, (a short) and instead of the wiring catching on fire a fuse will blow.................It is a safety feature.

If you must replace a fuse, after the first one has blown, in the hope that it wont blow again and it does there is a problem that needs fixing.

Doing it 3 more time has now caused the problem in the loom to migrate and do more damage. There is a good chance it has melted the wires to together. That is why it now blows when the key s turned on.

You need to diagnose where the problem is in the loom and then decide if it is worth fixing or replacing.

Do a continuity test. This will tell you where the problem is

https://www.xs650.com/threads/continuity-testing-made-easy.49917/

And yea, Welcome
 
There are good schematics in the tech section. On my 77, all the +12 when the key is on are brown it seems. You might start by looking at all connectors with a brown (or what ever your model +12) wire.
 
A fuse is in the wiring in-case there is a problem, (a short) and instead of the wiring catching on fire a fuse will blow.................It is a safety feature.

If you must replace a fuse, after the first one has blown, in the hope that it wont blow again and it does there is a problem that needs fixing.

Doing it 3 more time has now caused the problem in the loom to migrate and do more damage. There is a good chance it has melted the wires to together. That is why it now blows when the key s turned on.

You need to diagnose where the problem is in the loom and then decide if it is worth fixing or replacing.

Do a continuity test. This will tell you where the problem is

https://www.xs650.com/threads/continuity-testing-made-easy.49917/

And yea, Welcome
Thanks for the advice. First time at this so mistakes will be made.
 
Do not, and i repeat do not put any power through the loom/harness. Disconnect your battery and take it off the bike. All diagnostics can be done by continuity testing.

Your bike needs to be identified buy using the vin # and the vin chart. You will find a vin chart in the thread, (XS650 Model Identification/Year/VIN, Workshop Manuals, and Other Information) on the Garage forum.
Thanks for adding this. That was going to be my next question if the battery needed to be installed. Also what is the loom harnesses?
 
Thanks for adding this. That was going to be my next question if the battery needed to be installed. Also what is the loom harnesses?

Harness or Loom is the main part of the wiring that winds around your bike from the headlight to the taillight. All the wiring.

Honestly your best bet is to do some homework. Go to utube or do a google search and find some beginners courses to help you learn the very basics.

I don't have the time right now to post links to help with some of the basic info from here. I will do that later today.

Have to get a vin no so we know what bike you have and for you to get the right manual..................have to have a manual.

This is a quick pic of how a harness/loom and cables sit on a bike. This is not necessarily your bike
Standard fram 2_html_68224547.jpg
Standard frame 1_html_m39e75ab9.jpg
 
Also check resistance between the alternator rotor slip rings. A dead short in the alternator windings can cause the main fuse (the only fuse in the system prior to 1978) to blow.
 
Harness or Loom is the main part of the wiring that winds around your bike from the headlight to the taillight. All the wiring.

Honestly your best bet is to do some homework. Go to utube or do a google search and find some beginners courses to help you learn the very basics.

I don't have the time right now to post links to help with some of the basic info from here. I will do that later today.

Have to get a vin no so we know what bike you have and for you to get the right manual..................have to have a manual.

This is a quick pic of how a harness/loom and cables sit on a bike. This is not necessarily your bike
View attachment 209838View attachment 209839
Harness or Loom is the main part of the wiring that winds around your bike from the headlight to the taillight. All the wiring.

Honestly your best bet is to do some homework. Go to utube or do a google search and find some beginners courses to help you learn the very basics.

I don't have the time right now to post links to help with some of the basic info from here. I will do that later today.

Have to get a vin no so we know what bike you have and for you to get the right manual..................have to have a manual.

This is a quick pic of how a harness/loom and cables sit on a bike. This is not necessarily your bike
View attachment 209838View attachment 209839
This is the vin 447202877 and I have this manual (pic attached). I'll look up some YouTube videos for the basics. Thanks for your help!
 

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I have a ‘76 XS650C and the bike has only one fuse. Mine started blowing the fuse whenever I used the left hand turn sgnal and so I assumed it was the switch, or possibly the flasher or something with the wiring inside the headlight bucket…but nope.

If you look at each of the four turn signal stalks, they are attached with a piece of hollow threaded rod - and the power wire for the signal goes through that rod. The entrance to the hole in the rod - on the left rear turn signal - had a burr on it that had worn through the insulation on the power wire and THAT was causing the fuse to blow every time I used the LH turn signal.

Sooooooo……I took all the signal stalks off the bike and de-burred all of the threaded rod holes (both ends) - and then I put a little piece of heat shrink tubing on each signal power wire, and that cured the problem.

BTW - I found that two of the other signal stalks had the some danged problem but they just hadn’t gotten around to shorting out quite yet.

Pete
 
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I have a ‘76 XS650C and the bike has only one fuse. Mine started blowing the fuse whenever I used the left hand turn sgnal and so I assumed it was the switch, or possibly the flasher or something with the wiring inside the headlight bucket…but nope.

If you look at each of the four turn signal stalks, they are attached with a piece of hollow threaded rod - and the power wire for the signal goes through that rod. The entrance to the hole in the rod - on the left rear turn signal - had worn through the insulation on the power wire and THAT was was causing the fuse to blow every time I used the LH turn signal.

Sooooooo……I took all of the signal stalks off the bike and de-burred all of the threaded rod holes - and put a little piece of heat shrink tubing on each signal power wire and that cured the problem.

BTW - two of the other signal stalks had the some danged problem but they just hadn’t gotten around to shorting out quite yet.
Thanks for this!! I have the same bike!
 
^^^^ - that schematic is your best friend - print it out large format in colour and go for it.

As others have said - TAKE THE BIKE BATTERY OUT of the equation entirely and just use an ohmmeter to check whether connections and wires are in good condition.

You do not need an expensive meter - just a little $10 unit from Radio Schmuck or something like that will do the job just fine. The key thing is to work methodically and be organized.

Pete
XS650C_RHS-1.jpg
 
Thinking out loud here this can be difficult.
If I get this right
Cranks
Starts
Blows the fuse after a while ( at least from the beginning )

I would start in the direction Mr Grizid points out # 11
Servicing the charging circuit and as a first measure between rotor slip rings and then the rest of the charging circuit
there are Service manuals on line for measuring regulator rectifier stator and rotor
perhaps there please check

https://thexscafedotcom.wordpress.com/2011/01/10/xs650-manuals/

The 30 sec it ran did it run properly or banging missing shooting in exhaust or carburetor ??

A quick look at the wiring going into the light bucket ,,there should be a rubber grommet preventing the metal cutting into the wires.
Please inspect..
 
Thinking out loud here this can be difficult.
If I get this right
Cranks
Starts
Blows the fuse after a while ( at least from the beginning )

I would start in the direction Mr Grizid points out # 11
Servicing the charging circuit and as a first measure between rotor slip rings and then the rest of the charging circuit
there are Service manuals on line for measuring regulator rectifier stator and rotor
perhaps there please check

https://thexscafedotcom.wordpress.com/2011/01/10/xs650-manuals/

The 30 sec it ran did it run properly or banging missing shooting in exhaust or carburetor ??

A quick look at the wiring going into the light bucket ,,there should be a rubber grommet preventing the metal cutting into the wires.
Please inspect..
For the 30 seconds it ran it wasn't solid, it struggled to keep going sounded like it was struggling in the exhaust.
 
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