No electrical, no idea

[relempago]

Hey guys, I own a 76 cb750 which has been a great ride for the last year. I'm pretty decent with typical mechanical issues, but I am in over my head with electrical.
Here's the problem; I've got no power to start the bike. Nothing, no lights, no neutral light NOTHING. I assumed a bad main fuse, but that's not it. I have a fully charged battery, good fuses (checked, rechecked, swapped for new fuses etc) and I continuity through everything I've been able to check or understand how to check and get a good 12.20 where I believe I am supposed to. I've been going through the wiring diagrams for the last week, and testing with my multimeter, checking and cleaning connections, but I cant seem to track down whats the matter.
Whats more baffling is that at some point yesterday after checking connections and general fiddling; I turned the key and had power! Hit the electric starter, and it went back to dead. Retraced my steps went through it all again until dark and our San Francisco wind and fog rolled in and packed up for the night.
I feel like someone with more knowledge on this subject would have this wrapped up in an afternoon. I've been combing through previous posts, gleaning what i can, reading up every aspect of the cb750's electrical  and Im at a loss.
Any help or ideas would be greatly appreciated. I don't want to tow her to a shop for someone to go "here's your problem right here, that'll be $150". Also stubborn pride.
Thanks!

[hondacb750f]

sounds more like a loose wire than a bad wire.  I know nothing about wires. but I would try and check all the grounds.   I had a similar issue and it was ground related.


   also. try and wiggle the actual ignition switch.   just had the same thing happen on a riding mower, and every time we wiggled the ignition switch it would work.


 
        also you may have a 30 amp metal fuse,   which is just a piece of metal.  it  may have broke. on my 88 Honda, it was on the battery side. took three weeks to figure it out and 3.00 to fix it.

  good luck please keep us up dated.

[TOOLS1]

I would start checking the wires on the ignition switch, and then the switch itself.
TOOLS

[Re-run]

I vote on the ignition switch as well. Many times the connector wears out and the contacts dont make contact. It is possible the switch is bad too. It does happen. Or it could be dirty. Spray some contact cleaner inside the switch till it runs out clear.

[relempago]

Thanks guys, I tried to look at the ignition last night, and all soldering looked good, I had continuity though the switch. Even tried the jiggle method, to no avail.
Ill pop it off tonight after work and go through the wiring, clean it and see how she does. Ill let you know what I find.

[LukeM]

Here's how I fixed my son's friend's CB550, after he re-wired the whole bike:

Get access to as much of the wiring harness as you can (remove seat, gastank, open up headlight housing, etc).
Hook up your battery.
Turn key to ON position.
Using a small stick of wood (like a drum stick or similar), start tapping the harness until you see the headlight come on (I'm assuming yours is wired to turn on the headlight when you turn to ON).
Start at the battery, just tapping the wires.  Tap the fuses, and work your way around the harness.

What fixed the CB550 was the use of household heavy stranded ground wire (14ga, if memory serves), tied to a corroded ground lug at the frame. We replaced that wire with some automotive stranded (more strands, 16ga), cleaned the ground lug and where it met the frame, and voila!  All better.

Other possibilities:
Bad main fuse (the wire thing mentioned earlier)
Loose battery connection
Ignition switch (TOOLS)

Until you know what it is, it could be anything.  Be thorough.
Luke M

[relempago]

I checked the ignition switch last night, found continuity to the wire harness connection, and through to the switch both for red and black. I pulled the switch, checked continuity through red and black with the key being turned, worked as it should; no continuity when open, and good when closed. I took it in for the night and decided I would dissemble and clean it thoroughly. It seemed to be in good shape with minimal grime on any of the connections and the two small contact plates with springs were clean with plenty of push from the spring to ensure contact. Cleaned everything anyway, reassembled and still nothing...
I was filled with more than enough self doubt though..you guys were referring to the switch with the key correct? And not the right hand switch with the kill? I feel as though I hear people blur the lines when discussing to these two.
Also, and probably quite important, I left out a likely key fact that I neglected to mention due to my telling of this problem to too many of my buddies in person and forgetting that forum members can not read my mind: all of this began when I created a splice for my number 4 spark plug wire. I saw on another thread how it could be done to avoid buying a new coil. I have tested the coils and the seem to be good with a near 5 ohm reading on the primary and around 14 on the secondary. I feel like and idiot for not mentioning this.
I did notice when testing across my battery to ensure a decent charge, that it shows at 12.15 or so until I turn the key, then it drops to zero. I assume that its telling me that the overall circuit is not complete? Maybe a ground issue? Or is that just what its supposed to do?

Thanks again for any help

[relempago]

Also, LukeM

I loved the idea of this method, it really encapsulates my skill level with electrical. I pulled the side covers, tank, and opened up the headlight bucket. I fiddled and tapped everything in sight, even unwrapped dubious looking taped connections, cleaned, reconnected and re-taped....still not a flicker.
I did look over the few ground i know the location of but didn't see or read anything bad.

[TOOLS1]

Since it happened when you were working on the coil, I would bet the problem is in the wiring that is located around the coil. Start looking to make sure nothing there got disconnected, reconnected to the wrong place, or shorted. Do you have a wiring diagram for your bike?
TOOLS

[relempago]

TOOLS1,

I do have a wiring diagram, printed a few out actually, some better than others and I am becoming more comfortable with them.
I focused attention around the coils, everything seems well connected, cleaned up any then showed wear or grime, tightened any that seemed loose. There is a curiosity attached through the black and white line coming into the coils; a toggle has been added right before the coils. I assume this is some make-shift kill? I've not seen it before on any diagram. And yes i have certainly tried it both stations of the toggle.
I was debating if this is the sort of thing that needs to be cut out? But I'm hesitant to do so since the bike obviously worked for quite a while with it. and I wasn't sure if it is necessary, stock, a rigged thing etc.
I will check more thoroughly around the coils again tonight.

Thanks

[TOOLS1]

That would be rigged anti theft device. You know it sounds like your wiring harness has been pretty butchered. You might save yourself a lot of grief, and money by getting a new harness from vintagecb750.com and installing it.
TOOLS

[Re-run]

When you checked the battery and got 12.15 volts, that is a bit low. When you got zero volts, were the leads connected to the battery? If so, that is one bad battery.

[relempago]

Re-run,
Yea, the battery was charged to 12.49 two weeks ago. It has slowly dropped while sitting connected, turning the ignition on and testing. Does that seem like a bit rapid for drain?
When I tested with my multimeter just yesterday (red to positive, black to negative) I had 12.15. While keeping my test leads on the battery as described above, I turned the key and the battery would drop to 0. I had assumed (and probably naively) that this was indicative of a open circuit and that it meant that I was at least able to see results through to my ignition switch and that maybe the problem was further down the line?

[relempago]

Tools1,

TOOLS1 wrote

That would be rigged anti theft device. You know it sounds like your wiring harness has been pretty butchered. You might save yourself a lot of grief, and money by getting a new harness from vintagecb750.com and installing it.
TOOLS

Yea that makes sense for a anti-theft mechanism. Would it be smart to cut it out and purify that connection?
I was hoping to avoid a new wire harness, only out of intimidation, and a little out of cost,  but maybe you're right.

[TOOLS1]

Replacing a harness is a lot easier, and cheaper then repairing one.
TOOLS

[rich]

Battery! I got a brand new AGM once, it read 12.5 until you put a load on it, went right to .01 V. I hooked up another battery (good battery from my mower with jumper cables) and it didn't drop more than 1/2 a volt when I switched the key on.

So try something like that, you can even use your car battery, just don't have the car running.

[Re-run]

Right you are Rich. A battery should never drop to 0 when the ignition is turned on. A drop, yes but nothing this drastic. To be sure, take your battery into a shop and they can test it, usually for free.

[relempago]

Rich, Re-run,
Sounds good. I got off work a bit late and the local shops (Napa, O'Reilly, cycle shops)near my house had all closed, Ill drag the battery around with me tomorrow and get it checked. Here's hoping for a battery solution.
Thanks

[relempago]

Guys,
Took the battery in his morning, it checked out fine and was just a little low, both of charge and water. Charged it up and filled up the low cell, popped it back in my bike and turned the key....
To my surprise, everything came on, all lights, the display, kicked it over a few times got it started, but it died (forgot the choke). I was stoked until I decided to try and start it using the electric starter. Twisted the throttle a few times, threw the choke, pulled in my clutch and hit the starter.... heard a small click and everything went dead. No lights, no neutral light on the panel, no anything.
I'm not sure if I blew a fuse, I was already running late for work at this point and couldn't check. It did strike me though that both times I got a flicker of life was after I hooked up the battery after having it disconnected for short period of time.
I'm not sure where this leaves me at all. I seem to have all the necessary components for a functioning motorcycle but.....
Any one have a clue?
Thanks again to everyone who keeps helping me deal with this.

[TOOLS1]

Sounds like a bad connection at the battery, or a bad cable.
TOOLS