Topic: Bike cut off while riding, now has zero power (electrical - CB750)

[Eddie750]

Bike: 1975 CB750. Stock.

I got out of class tonite and it had been raining, the bike sat in a light drizzle for maybe 30 minutes or so uncovered. I got on the bike, and she fired right up, no issues. While riding home I was turning on to the interstate and all of a sudden my lights turn off, dash gos black, and the bike cuts off. I pull to the side of the road, turn the key off, turn it back on and nothing. The bike has zero electrical power. No lights, gauges, dummy lights, etc. I checked battery connections, as many wires as I could with it being dark, and all I had was a cell phone for a light. I wiggled all the right wires in the right places. But still nothing. The bike will not kick over either. I caught a ride home and I will be heading out first thing tomorrow to give it a look over. Trying to get an idea as to what it might be.

The only time I have ever seen a bike completely lose power like this is either with a dead ignition or dead battery, it cant be the battery because it happened while I was riding, and I had only gone maybe 2 miles from class when it suddenly cut off while riding, so I couldnt have run the battery dead anyway.

Is it probably just rain water down in the ignition switch? or can an ignition switch suddenly just go all of a sudden while riding?

My list of things to try tomorrow so far:

- Check all connections, wires, grounds, etc to make they are clean and dry.
- test the battery
- re-check all fuses


anything else? If all else fails I'm thinking I should just bypass the ignition and see what that does, i did this on another old honda and it worked fine until I was able to replace the ignition switch.

I'm not a mechanic so any help would be greatly appreciated. Thanks!

eddie

[Spanner 1]

Didn't hear you say anything about the fuses  ... did you check the main fuse ? Humid conditions ( rain ) could make the main fuse 'go over the edge' and fail . Ever polish the fuse holders  for good connection ? Lots of posts here about making your electrical really reliable... very important if you ever want to ride any distance... if your radius is 10 miles then just replace the fuse and carry-on, good luck  

[Eddie750]

Didn't hear you say anything about the fuses  ... did you check the main fuse ? Humid conditions ( rain ) could make the main fuse 'go over the edge' and fail . Ever polish the fuse holders  for good connection ? Lots of posts here about making your electrical really reliable... very important if you ever want to ride any distance... if your radius is 10 miles then just replace the fuse and carry-on, good luck  

Sorry, yes I did check the fuses. Pulled the left side panel and checked all 3. they were fine. connections were good and I could tell that the fuse holders were all changed by the PO, they looked brand new. Unless there are other fuses on the bike I am unaware of, then the fuses checked out. The ones I checked were inline behind the left cover, 3 of them, red wires.

[nancy]

1st time (and the last time) my 750 wouldn't go - Spanner1 came to my rescue and gave me the right oil. Listen up.
I'd second his 1st choice of suggestions too. Most likely common denominator between ignition, lighting, et al = fusing.
regards
Mark
PS: Still owe u a beer spanner.

[Eddie750]

1st time (and the last time) my 750 wouldn't go - Spanner1 came to my rescue and gave me the right oil. Listen up.
I'd second his 1st choice of suggestions too. Most likely common denominator between ignition, lighting, et al = fusing.
regards
Mark
PS: Still owe u a beer spanner.

fuses checked out. im thinking ignition?

[Spanner 1]

Eddie, sorry didn't mean to come out fighting  ... but a simple bulb tester under the seat can prove everything you would ever need to know about your bikes electrical.. vis; is there power both sides of the main fuse ?.. it's common for a fuse to fail under the cap so it 'looks' fine and still fused to the eye. Sudden 'no power' is always a fuse or the ign. switch ( don't think so in your case ).....IMO.

[Eddie750]

Eddie, sorry didn't mean to come out fighting  ... but a simple bulb tester under the seat can prove everything you would ever need to know about your bikes electrical.. vis; is there power both sides of the main fuse ?.. it's common for a fuse to fail under the cap so it 'looks' fine and still fused to the eye. Sudden 'no power' is always a fuse or the ign. switch ( don't think so in your case ).....IMO.

No worries

I almost always have my tester on my, but I took a few tools out of my bag the other day and forgot to replace them. And with the rain and it being dark, I didnt have many options on the side of the road. It was right about parts store closing time too.

Tomorrow is a new day, and the first thing I will check is all 3 fuses again, and make sure they are getting power on both sides of the wire. If they check out. I will test the ignition switch (or at least have my friend talk me through it on the phone haha). I think the worst case scenario will be a ig. switch bypass. best case its a wire or a fuse.

[Spanner 1]

Eddie, if the main fuse is O.K. then to bypass the ign. switch 'jump' the red wire at the switch connector to the black wire at the connector = same as turning the switch 'on'.... good luck. If this works and the bike starts etc. then look at the tail-light, if working then O.K., if not then 'jump' the brown wire at the switch to the brown/white at the switch.......hope it's just the fuse tho'....

[Grnrngr]

Had the ignition switch on my 72 xs650 "go bad" more from being covered with snow for a few days rather than a little 1/2 hr of rain, but when it went, the first thing it did was blow the fuse...and I've had several fuses do what Spanner said, look good but be broke under the endcap, a couple of them even took a long time to replace, the cap came off inside the holder, filament looked good but no cap on the end, it was stuck inside the long skinny part of the holder and the wire was too short to push it out the open end of the fuse holder, had to cut and splice the wire......good luck!

[Eddie750]

thanks for the tips guys!

Ill keep you posted on my progress after I go on the rescue mission tomorrow.

[ekpent]

If the fuses check out OK then check under the tank where the ignition switch plugs into the harness. Sometimes if the switch gets relocated,like up tp the handle bar area for instance it can be a little stretch for the wires.Had one come loose there while riding and everything went dead.

[Eddie750]

Turns out it was the ignition switch. I bypassed it and she lit up.

Putting a new one in Sunday, toggle switch till then.


Thanks for all the input guys!


eddie