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Discussion Starter #1
My cb250 has an issue with electric power. I have it jumped off a car with the motorcycle battery removed. I have inspected the entire harness and everything works except for the speedometer backlight. I had accidentally shorted the positive on the starter relay to frame ground (it fell) and at that instant the power cut out to everything. The starter switch power through is working and the key switch ignition is also working. I read 12v on the ignition switch until I turn on the ignition when all the sudden, anywhere I should see 12v to ground I see around 0.4v. For some reason when I run it off a 1 amp 12v wall converter all the lights work well. It seems to only not work when jumped off the car battery.

Just as a sidenote, I replaced all the fuses and it all worked before I shorted it.

Anything you can tell me could help!
 

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Well if it works off your 12v adaptor but not the car battery you have some possible issues with the battery.
1. Battery polarity may be connected wrong.
2. Battery is now a paperweight.

Do you have a test meter or test light?
Also you could take the battery to an auto parts store and ask them to load test it.

By the way if you ever need to jumpstart a bike from a car, do not have the car running.
 

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Discussion Starter #3
Thanks for your reply Alan! I have a multimeter, can I rig up a load test with that? Also my car starts and runs well electrically.
 

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As Alan F indicated, jumping a bike with the car's engine running can damage the bike's electronics. There's plenty of amps in a car battery to jump the bike without draining the car battery.
 

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Well if that battery works in your car, it's a good battery with a full charge.

I'd remove and test your fuses once more to be sure.
Apart from that I'd try unplugging everything from the harness and testing one thing at a time as you add things back. Also make sure all of your frame grounds are clean and tight.


I'll be performing these types of tests on one of my 250 Nighthawks soon. I've got 3 and I've been putting one together as a test bed for electrical system parts, carbs and to get the 3 engines some run time after I've made sure of the basics.

You said you inspected the harness all over, all connectors clean and tight?
 

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Discussion Starter #6
Hey all, thanks for the helpful replies.
I used my multimeter to find that the negative lead of the jumper cable had formed corrosion between the wire and the clip. It could transmit voltage but not current.

Long story short, I fixed the jumper cables and now the bike works fine...

So sad, my bad.
 

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Glad you got it figured out and fixed.
 

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Wow, good catch. I'll go ohm out my 40 year old jumper cables...
 
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