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Electrical Help required for newbie…please

Jim1973

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Hello all, I'm Jim and I have been working on a 71' CB750 K1 as my first project - if anyone is interested you can see it here (shedcustom.worpress.com). I have relatively comfortable finding my way around the mechanical stuff but when it come to electrics I struggle so would really appreciate any help anyone can give - so here's my problem.

I last rode the bike about 6 months ago as I've been working on it over the winter, I have come to start it and there was nothing. I have had the battery on trickle charge over the winter so thought it would be ok. The headlight and brake lights came on but it wouldn't turn over the reading from the battery read about 12.7v but when I turned the ignition on it dropped to 8.6v so thought it may be the battery so I have just replaced it with a new one. It still won't turn over and now only the neutral light will come on the headlights, brake lights horn etc now do not have power and I have tried hooking it up via cable to a car battery to see if that helps - it doesn't still on the neutral light. I read in another thread about bridging the solenoid terminals to see if that works - i got sparks and it turned over - thats as far as i have got - does this make sense to anyone…please?

Thanks

Jim
 
If Your lights work theres a way to check the solenoid, But since You said Your lights ect. do not work I would look at all wiring connectors (loose, burnt,) If everything else worked disconnect the yellow/red stripe wire and black wire at the solenoid use a test light or meter and connect across the two ( Not the ends going to the solenoid but the wiring harness) with the key in the on position the light or meter will give You a reading when the start button is depressed if not the solenoid is bad, Never connect a car battery to Your bike You could damage the rectifier. Good luck
 
Had a similar problem. Everything worked fine until one day, nothing! I put the leads of a multi-meter across the main fuse to measure and !! good as new. Loose connection at the fuse box.
 
Thanks Dan- i've spend most of the day in the shed today trying to figure it out - i've cleaned the switch and fuse connections and i have strong lights now which is an improvement but i've got nothing from the starter - it will only turn over when i bridge the solenoid terminals. I don't have a multimeter but am going to get one tomorrow and i'll try your suggestion - i'll let you know
 
Jim, Just pick up a inexpensive 12vdc test light it will be sufficient to test the problem You are having. I use both for different problems.
 
Jim,

Amazingly I am having the EXACT same problem with my '82 750f. Solenoid, starter switch, main wire harness and rectifier are all brand new. Checked and cleaned up grounds, Fuses are all good, have power to the starter from the solenoid but the bike will only turn over when I jump the solenoid. When I hit the start button the headlight dims, but that's all that happens. I'm completely stumped. If you or anyone else has some advice I'd love to hear it because I'm out of ideas.

thanks,
 
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