Main fuse blowing...Sometimes. Need Advice.

[Hardfahrer]

My main fuse is blowing but not all the time. 82 xs650. Started last season when I was on a ride. I was traveling home after many hours of riding and the bike shut off. Found the main fuse to be blown. I tried replacing it and it blew again. After about 20 minutes I tried another fuse and It didn't blow and got me home (About 40 miles) Had a few rides after that and had the fuse incident maybe one more time where the bike shut off and I put in another fuse and it blew and after a while it would take the fuse and I would be able to ride home. Going on a shakedown run this season, I got the bike out of the garage and on the road, began to rev it out in first and into second and the fuse blew again. I pushed it back to the garage, replaced the fuse and it started back up. Now, and I've repeated this a few times, when I rev it up pretty high, it will blow the fuse. Not all the time but it's fairly repeatable.
I find it difficult to test for a short because it's not a dead short. I had replaced the rotor a few years back with a rotor from MikesXS. I tested the rotor and got 5.1 OHMS. Open circuit from each ring to ground. Battery voltage is 14.7V at high rev so the charging system seems normal. Did a slap test and it worked well enough. Tested the voltage at the battery and the voltage at the rotor wire and they were within .2V so no short there. Tested the stator resistance on the 3 white wires and they were consistent but I forget the exact reading at this point. I tested the 3 white stator wires at idle and am getting 10.6V to 10.7V AC at each combination of wires so that checks out. I'm getting 14.3 Megaohm resistance from the 3 white stator wires to ground which isn't an open circuit, but it's close, so that looks good.
The bike is heavily modified with different headlights and led turn signals, and most of the safety switches have been bypassed. I have an upgraded fuse box with blade type fuses. The safety relay is intact and working, The reserve lighting unit is removed. I'm running the pamco ignition with e-advancer. The stator and rectifier/regulator are stock. All of these mods were in place well before the fuse blowing started happening.
I'm kinda at a point where it's above my pay grade so I figured I'd try to take it to the forums. Are there any thoughts on what would cause this or is there a good procedure to isolate where it might be? Any help is much appreciated. I read that rotors do funny things, I imagine stators can too. I don't mind buying the new parts if it were a stator or rotor, I just don't want to throw money in the wind if I'll still be left on the side of the road fingering through my bag of extra fuses.
Bit of a side note, I bought a replacement rec/reg from xs650direct , because rectifiers go bad and I figured it might be or will be a problem. I plugged it in and my headlights didn't work. Plugged the old one back in and everything is fine. Regulator was bad out of the box it seems. I got a refund and I don't recommend the regulators from xs650direct.
Thanks again for any advice.

 

[Jan_P]

Taking this out of memory
Please upload or describe the actual wiring
If the main Fuse Blows and not other fuses the ( Out of memory )
fault is in the wire to the ignition lock and back to the fuses
Or in the few lines before (Upstream ) the rest of the fuses
Depending on model but if I remember correct the starter ,and perhaps alternator
Going into the headlamp is sharp edges that can cut into the wiring.
But please upload wring ..

 

[jetmechmarty]

I had the same issue on a 2000 mile trip almost 20 years ago, 1983 XS650SK. The main fuse opened three times. One of those times I was going down a long, steep grade near Morganton, WV. The bike got me home. The next time I rode it after the trip, the battery went dead and the bike went home in the truck. The rotor was dead short. After replacing the rotor, I have not blown another main fuse, ever.
Since the replacement rotor is a Mike's XS unit, I would look no further if it was my bike. I'd put a rewound OEM rotor on it without question. @Jim can hook you up.
YMMV

 

[gggGary]

I like to open the headlight shell and check where the wire bundles go through the grommets at the back . I have found several grommets old and torn allowing the sharp bucket edge to cut into and short a wire. The wires to-from the iggy switch are protected only by the main fuse.

 

[JRay77]

Re wire the whole thing. New fuse box and all. Those wires are 40+ yrs old. Been hot. Been cold...dry rot. Cracked insulation. Shorts are gonna happen. Sounds like start wiring after charging system with reg/rec fwd.

 

[Hardfahrer]

 

[Hardfahrer]

 

[Hardfahrer]

 

[Hardfahrer]

Jan - It's the original wiring, like the schematic above, from the 82 XS with a few items deleted or bypassed. I bypassed the ignition switch and put in a toggle, all the old speedo wires are disconnected (neutral light etc.) I get good readings from the wires when it's not running. No shorts. It's only when it's running and higher revving that the fuse blows. Doesn't blow all the time though.
JetMechMarty - I may go that route even though rotor and other charging system tests check out. But what if it's the stator somehow? I'll be miffed.
gggGary - it's not the original lighting can. I put on an ammo can for the lights and put in new grommets. I did recheck the grommet area however and found everything to be in good order. I then turned on the ignition and shook and pulled every wire on every part of the bike to try to blow the fuse and got nothing. Before pulling on the wires, I put a 7.5 amp fuse in the main slot to make it easier to blow. I also started an ran the bike and revved it to try to blow the 7.5A fuse but it wasn't cooperating. Couldn't blow the fuse.
JRay77 - the bike spent most of its life in a garage not being ridden, and as a testament to that, the wires are still pretty supple. I'm not ready to go the full replace yet, but it's not ruled out. Thanks.

Anybody think its a good idea to put a fuse inline with the blue wire and the brown wire after the ignition connection to further isolate what circuit it might be? Will that work? Then if it's the brown wire, put a fuse inline with the brush circuit and the rectifier circuit to further narrow it down? I hate to cut into the wires to fuse the individual circuits as it is then just another problem point down the road but I don't have any better ideas.

Thanks for your responses and again, any advice is appreciated as I am still chasing this.

 

[XSAndy]

My main fuse is blowing but not all the time. 82 xs650. Started last season when I was on a ride. I was traveling home after many hours of riding and the bike shut off. Found the main fuse to be blown. I tried replacing it and it blew again. After about 20 minutes I tried another fuse and It didn't blow and got me home (About 40 miles) Had a few rides after that and had the fuse incident maybe one more time where the bike shut off and I put in another fuse and it blew and after a while it would take the fuse and I would be able to ride home. Going on a shakedown run this season, I got the bike out of the garage and on the road, began to rev it out in first and into second and the fuse blew again. I pushed it back to the garage, replaced the fuse and it started back up. Now, and I've repeated this a few times, when I rev it up pretty high, it will blow the fuse. Not all the time but it's fairly repeatable.
I find it difficult to test for a short because it's not a dead short. I had replaced the rotor a few years back with a rotor from MikesXS. I tested the rotor and got 5.1 OHMS. Open circuit from each ring to ground. Battery voltage is 14.7V at high rev so the charging system seems normal. Did a slap test and it worked well enough. Tested the voltage at the battery and the voltage at the rotor wire and they were within .2V so no short there. Tested the stator resistance on the 3 white wires and they were consistent but I forget the exact reading at this point. I tested the 3 white stator wires at idle and am getting 10.6V to 10.7V AC at each combination of wires so that checks out. I'm getting 14.3 Megaohm resistance from the 3 white stator wires to ground which isn't an open circuit, but it's close, so that looks good.
The bike is heavily modified with different headlights and led turn signals, and most of the safety switches have been bypassed. I have an upgraded fuse box with blade type fuses. The safety relay is intact and working, The reserve lighting unit is removed. I'm running the pamco ignition with e-advancer. The stator and rectifier/regulator are stock. All of these mods were in place well before the fuse blowing started happening.
I'm kinda at a point where it's above my pay grade so I figured I'd try to take it to the forums. Are there any thoughts on what would cause this or is there a good procedure to isolate where it might be? Any help is much appreciated. I read that rotors do funny things, I imagine stators can too. I don't mind buying the new parts if it were a stator or rotor, I just don't want to throw money in the wind if I'll still be left on the side of the road fingering through my bag of extra fuses.
Bit of a side note, I bought a replacement rec/reg from xs650direct , because rectifiers go bad and I figured it might be or will be a problem. I plugged it in and my headlights didn't work. Plugged the old one back in and everything is fine. Regulator was bad out of the box it seems. I got a refund and I don't recommend the regulators from xs650direct.
Thanks again for any advice.

Had the same thing happen to me. First short term fix was cleaning the contacts in the fuse box but the ultimate fix was replacing the rotor. I think this could be an early warning sign of a rotor failure. Test it and see if it’s struggling. Especially if the contacts are good.I later got to the point where my battery stopped charging and things became more obvious.. My contacts were getting so hot they were melting the fuse box. Ultimately in my rotor diagnosis and fix I ended up putting a NOS wiring loom into her too.