1981 XJ750 Seca Intermittent Shut down

HELP! I had to push my bike home tonight! Hopefully I can properly describe what's happening.
Four days ago I was out on the bike and it just shut down while running. I thought it was just a one off quirk.
Tonight, while warming up, it happened again. I shut the key off and back on and it started up fine. This happened again before I headed out. Same procedure and I headed out. My first stop was only about 4 km away and the bike died 2 more times on the way. It happened again while idling in neutral 2 more times. I decided to try and get back home as it wasn't far. I made it two blocks away and it just cut out again, I coasted off the road and shut it off. This time it wouldn't reset. When it shuts down its as if I hit the kill switch. The headlight goes out and there's no power. The start button is non responsive. The only thing is the cluster backlight stays on. In the beginning I just turned the key to off and then back on and the self test would start, neutral indicator would work, kickstand light worked and starter button fired her up no problem. In the end turning key off and back on wouldn't work anymore. No headlights, but the cluster background lights would be on.
There's no rough start, no sputtering, no rough running. Just a clean and sudden loss of power and engine cuts out.
A few things out of the ordinary which may or may not be related to the issues. This week the kickstand switch failed. The warning light stayed on when I lifted the stand. I removed it and did a thorough cleaning and reinstalled it. It seems to be fine. A little over a week ago I was in a serious rain storm. More rain than the bike has ever seen with me. So it, and I, got a good soaking both highway and city riding.
I checked the battery tonight and its at 12.73v I put the charger on it. I cant see that being the issue. So...anyone have any ideas?

 

Do you still have the original fuse panel and glass fuses? The clips that hold the fuses get the tiniest bit of corrosion and contact is lost. Then when you attempt to clean them or move the fuses the clip breaks off. The answer to this problem is to replace the fuse panel with a blade type fuse panel. Len at XJ4EVER.com (his link is the logo in the top right corner of this forum page) has a kit just for this. Or go to any auto parts store and get a panel and fuses and make the swap. Worth while even when you are not having problems but very likely this is an issue for you.

 

Sounds like an electrical issue as @Fuller56 said. Those old fuses need to go. It would also be a good idea, if you have not already, to go through the wiring harness connectors. Take them a part one at a time, inspect them, clean them and put them back together. The ground wire and positive wires from the batter to the frame and starter should also be inspected.

 

^^^^ good suggestions

Another thought is the ignition switch because it is a two pole single throw. One side pretty much runs the bike and the other side powers the park illumination - the meter light and the license light. Since you are losing all power except for the meter light (and maybe license plate) I would suggest the ignition switch is at fault and if the above produces no joy then look at cleaning the switch .

If you have it in a failed condition you can check at the fuse box - the main fuse will have power in from the battery that goes to the ignition switch that is always there. The other 3 fuses should have power when the ignition switch is turned to on.

https://www.xj4ever.com/clean and lube the ignition switch.pdf

 

Thanks for the reply. The previous owner upgraded the fuse box to individual blade type fusses. I did check all the fuses and they all look fine.

 

Thanks Timbox! I will check all these items you mention. I did check a few connections at the side of the road in the dark but nothing made a difference. I will get into these things this morning.

 

Thanks Rooster. This gives me a place to start. I am not sure if the licence plate was still illuminated. I will check it out this morning. I can give it an hour before heading to work. Hopefully I can get this figured out before the weekend! have a 2 day trip planned!

 

Check the wiring loom where it/they pass around the steering neck. Not uncommon to find wear and tear (shorts or breaks) in the wiring there on 40 year old bikes.

 

ok..... so I started with the ignition switch. Pulled it out, took it apart, cleaned it, reassembled and installed it. It took me almost al day! Then IT STARTED!! Ignition switch feels better than ever. So I took it for a ride close to home. Circled the block quite a few times. Then got brave and took it for a longer ride. Made it home.
There was one thing that made me wonder though. At one point while changing gears the warning lights flashed on and the bike did its self test! Thats not normal! But.... it all seemed fine! I just got home from work and the plan was to run it and check some wiring while it was running just to make sure it wasnt something else. I started it up and no problem. Was letting it warm up and about 3 minutes in guess what happened??? Yup, it just shut down! Same thing. So it looks like I am now going to go through as much wiring as I can access.

 

All four cylinders gone at once, is the black ground from the pick up coils chaffed and touching the frame?

 

Yes. Bike completely loses power in an instant. Like using the kill switch. No sputtering or rough running. Even headlights out. Only power remaining is to the cluster backlighting and license light.

 

Next time you get it started wiggle all the wiring you can see if it cuts out, sometimes this helps in finding where the fault can be. Sounds like an intermittent ground wire fault although I am no expert.

 

If you turn the key on, get your DMM out and you don't have power to the HEAD, IGN, and SIGNAL fuses but do have power on the MAIN fuse then the ignition switch or its associated wiring is bad - it's a pretty simple test and always good to say yes, I see what is missing.

 

Im going to go do this now. I just had it running and moved around every wire I can reach without pulling the tank. Nothing happened. I guess even though I cleaned and reinstalled the ignition switch it doesnt mean that its still not faulty. Im trying to think logically as to why there is still power to the cluster lights and license plate light and no power to anywhere else??!! So power has to flow through the ignition switch. So main fuse feeds the ignition switch and then the ignition switch wire runs back to its own fuse. Is that correct? so no power to that fuse then ignition switch not sending power. I think thats basically what you just said!

 

Yes, in fact you can easily hot wire these bikes by installing a jumper from the main fuse to the input side of the other three fuses. For troubleshooting if you do this you want to be careful that you don't bypass the fuses, so the main fuse output side needs to jumper to the other 3 input side - if I remember correctly the 750 Seca it would be the back of the fuse box for main output to the front for the branch circuits that run the bike.

 

I will be back at it tomorrow morning.
So.... If the issue is the ignition switch then I could bypass the Ignition switch? I have a 2 day trip planned for this weekend and Im sure I wont get a replacement switch by then. Is this a bad idea or would be ok for a few days? Kill switch would still shut down engine?

Also, I will need to look at a wiring diagram and figure out input and output. The PO changed out the fuse box and put in individual blade fuses with their own little waterproof enclosures. He used all red wire for everything and its all taped up. I will have to open it up and figure out whats what!
Also... I have two 10a fuses, one 15a fuse, and one 30a fuse!

 

Hopefully that is all done well - I might jump in and blame the PO there but if the meter lights and license light remain lit then it is fair to say the main fuse and connections are still OK.

You might try working at the ignition switch connector instead of messing with the tape if the PO's work looks well done. On the ignition switch three pin connector check R in from main fuse, and then L and Br out. The Br out is the wire that feeds the 3 fuses to run the bike. There is a two pin connector also part of the ignition switch that is used for the battery monitor, so that warning will display if the ignition switch is not used.

The kill switch would still kill the bike, but I wouldn't necessarily recommend riding that way unless you have a full proof jumper that is large enough and well insulated with the seat closed to be safe.

Pretty sure stock is three 10 amp and the one main 30 amp - maybe the PO added something for the 15 amp??