Electrical gremlins - blown main fuse, melted connectors, bad neutral switch, and dead turn signal


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San Jose, United States
New to the XS650 scene and new to the forum, but I've learned a lot from you guys while I was battling the above mentioned issues. As somewhat of an introvert I never felt I had a good enough handle of the causes to ask a question here, so I'm just here to share my experience.

Bike is a 1980 Special. Bought it for under $2k from a local air force lady.

The first and most obvious problem is the main 20A fuse blows upon key on engine off. After removing the headlight housing I quickly determined the brown wire is shorted to the ground somewhere. The painful reality is that wire runs everywhere. During the process of elimination I found the big 8 pin connector from the rectifier turned brown and crispy. Being too mentally occupied to chase down the real cause of the short, I ended up cutting apart that connector and just soldered the wires together.

After maybe an 8 hour of searching, measuring, tinkering and thinking, and two more blown 20A glass fuses, I tracked the problem down to the rotor area. During that process my trusty multimeter became my BFF. I took of the stator/rotor cover and found one broken brush (just who designed the darn thing? you have to twist the little backing plate 180 degrees to install it correctly). When the new brush sets finally arrived, I took off the rotor for further inspection, and finally found the short - insulations on the 3 (or 4?) wires running into the stator have mostly been worn through. There is no grommet to protect them. For now electrical tape and zip tie will have to do. I will probably cut a section of automotive wire sheath to protect it.

Now I can finally start to bike and use some voltage measurements on the bike. The neutral light has thus funky blue/yellow color that doesn't change no matter what gear I'm in. At one point the bike jerked into my RC51 and almost triggered a katana sword fight. The issue was quickly found to be the neutral switch. I took it out and pressed the button on the bottom, the resistance between the wire and the threaded portion remains infinite. With some experience working on transfer case switches on some Japanese off-road rigs, this doesn't feel right. Please let me know if I'm wrong. I'm waiting for a used neutral switch from eBay.

Now the bike has come back to life, I found the right blinkers, both front and rear, don't work. After reading some forum posts my attention was naturally drawn to the controversial self canceling unit and the blinker relay. I swapped out the stock replay and replaced it with a electronic one (had to use two zip ties to make sure it doesn't slip out of the cylindrical housing), but still couldn't make it work.

After reviewing the wiring diagram carefully, I realized any issues with the self cancelling circuit or Reed switch are left-and-right blinker agnostic, which means any issues within those circuits would have done to same to left and right blinkers, which is not what I was dealing with. After more resistance testing between the brown and dark green wires, headlight housing mounted black wires, and engine ground, I couldn't figure out what went wrong. Here is another question: all the back wires in the headlight housing have roughly 0.9ohm resistance to the engine ground, which seems high. Anyone cares to opine on this?

I left my garage last night in disgust. As I was laying on my back it dawned on me: I can hook up my probe tester to force a 12V into the dark green (right blinker hot), and see if the right blinkers, front and rear, light up. I rushed to the garage as soon as I dropped off my rug rats this morning to try it out. Alas, both blinkers lit up beautifully. Now the only possibility is the blinker switch on the handlebar. Who would have thought the last gremlin is hiding in the beefy looking device?

After taking it apart I found a ground solder has broken off. Someone before me must have taken a piercing probe to track down the problem, because I saw some tiny holes on some wires; that someone was too lazy to take a couple of screws off to reveal the brown, dark green and black wires though, so the broken solder was never discovered.

I dumped a pool of solder into the pad and reattached the black ground wire. Voila, everything is working.

It took some sheer determination to take me this far, and I'm feeling pretty good about myself now. I hope this is helpful to someone who read this far. In hindsight I should have used the probe tester much earlier. It would have allowed me to test a whether a particular connecting point is grounded quickly, and even safely send a 12V to a spot without busting a fuse.

Want to thank all of you in this community for helping me along this journey.
These are old bikes so one of the first things you need to do when you get one is go through all the wiring. I start at the tail light and work my way up into the headlight, cleaning and repairing any bad wires and/or connectors. I've always found a few.

Being a 1980 model, what you are calling the rectifier is actually a combined regulator/rectifier. I wouldn't leave it wired in direct like that for long. Get a replacement plug set for it.
On the subject some input Maybe for the tech section .

The first thing to do always is to measure Voltage Across battery off and on and revving
Many have been chasing carburetors faults ..multiple times when this measurement that takes under 3 minutes and can be performed without getting out of Your Sunday Church suit.. Would have found it.

I have used soldering wires ..the problem is mostly in the connectors or switches the soldering gives a secure connection it takes less space and with some Shrink wrap I don't get problems . If disconnecting is wanted just cut it with a cutter mark it up first. Should one want connectors .Which is expensive and needs d tools this can come later.
When the machine is up and running

Voltmeter on the motorcycle is something one wants if not at once after the first stop out there Walking home or Taxi or Friend or Wife ,, Which then in 9 times of ten brings up the subject of selling the damn thing.

Electrical fault finding is different from Mechanical since the fault can be Temperature and Vibration dependent Not always there .So if unexperienced it may not be the best choice to tear down a wiring. Especially if the goal is to get it running in an evaluation period.

With experience one can go to the most likely faults and that experience is found here on the forum . If asking the answer probably comes

Mr 5 T is correct as always .but if we are talking a banged up cheap bike with a lot of miles on it. That you are not sure about .Put i in a lot of money time for a new wiring. Being inexperienced can be wasted money if there us something else wrong

Once the bike is up and running I am all for getting it better and better But at the start up period ..it can be best not to go all in
Yes, there are only a couple grounding points on the bike, one for the negative battery cable of course, and a small ground wire coming out of the harness up around the coil. You want to make sure the eyelets on these wires are clean, as well as the spots on the frame they connect to.
I also liberally coat the cleaned eyelet and the spot on the frame I wire wheeled the paint off with copper anti-seize. This protects it from corrosion and the copper in the anti-seize helps make a good connection.