Topic: black wire on voltage regulator 1976 CB750

[TwoTired]

I'm going to have to look for my moving box with my MC manuals to check what Honda published for the CB750.  I don't trust the Clymer wire diagrams.  Not sure where that box is.  I'm still setting up my shop.

Are your bar wires internal or external?  Which is the new switch you installed?   Perhaps check for shorts in the bars.  Loosen the switch you installed and insulate it from the bar.  To save fuses, put a headlamp wired in place of the fuse.
  But be fast if you see any smoke.  The headlight should limit the current into a shorted circuit to about 5 Amps.

Cheers,

[davidp1054]

Thanks two tired,
The new switch is the right hand with starter button and run stop with 5 wires.
Black/red, yellow/red, two blacks, and a black and white. The sheathed cables are internal in the bars.
The yellow /red, black/red and one of the blacks are the starter switch, and the black/white and the other black are connected in the run switch to allow power to the coils.
So far I have taken all 5 switch wires from the wiring loom and checked that they are not grounded.
The starter switch wire function as the should and the stop run wire are connected until you switch the run switch to stop which it should.
There is no shorts to each other or ground.
If I plug all wires into the loom the fuse blows, but if I don't fit the black wire there is no spark I assume
The black wire is the power.
I disconnect the yellow and blue wires at the coils and the fuse blows.
I then disconnect the black wire from the reg/rec and everything went back to normal with a spark
So I started the bike, the fuse blew,
The stator checks ok to all the paper work I have but is it possible that the stator has an intermittent issue?

[TwoTired]

The charging system does not get any power through fuses.
Consider the possibilty that run vibration makes your intermittent short connect.
I wonder if you insulate the bars, if a test run would pass without a fuse failing.  Working theory is your bar internal wires or switch components make intermittent contact with bare metal of the bars.

Still looking for my honda manuals. Fyi

Cheers,

[davidp1054]

Understand,
I will isolate the switch from the bars and see what happens
Many Thanks

[my name is nobody]

Try unplugging the 4 black wires in the 4 way connector in the headlite shell. then unplug the black/white wire coming from the kill switch and jump the harness end of that connector to the 4 way black that you just unplugged from the others. That will electrically isolate the front of the bike from the rear. I'm thinking the bike will still kick start,  (not with the starter motor) and if the fuse still blows, the short/or problem is somewhere towards the rear of the bike, and you can go from there.
If this is incorrect, and I read the diagram wrong, please correct me, just seemed like it might save some time. Can only find
k5 wiring diagram, k6 is not good quality ...Make sure all your ground connections are clean/tight..

[davidp1054]

I will try that tomorrow thanks,  it should get me a little closer.
I still can't find the fault, wiggle wires shake the coils the fault disappears I start the bike and the fuse blows again.

[davidp1054]

Hi Two Tired,
I have removed the switch from the bars and the fault is still there.
The fault intermittently disappears but once the bike starts the fuse blows.

[Robbo]

How old/worn is your key switch?  Do you have a spare that you could swap in?


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[TwoTired]

Hi Two Tired,
I have removed the switch from the bars and the fault is still there.
The fault intermittently disappears but once the bike starts the fuse blows.

Can you report with confidence that the bar internal wires aren't chafed and making bar contact?

One step at a time...

Cheers,

[davidp1054]

There is no chaffing of the internal wires, there is no grounding of any of the wires, and the switch is wired and works as it should according to the drawing and also a video on utube showing the switch function. The wiring loom is new.
The coils are mounted on an aluminium frame bolted directly to the bike frame, does the coil mounting bar which passes through the coils have to be isolated from the chassis?

[davidp1054]

Hi Robby,
The ignition key switch is also new from David silver.
The bar switches are new, the reg/rec is new, the fuse holder is new, and the wiring
Harness is new. Any suggestion gratefully received.

[Robbo]

Hi Robby,
The ignition key switch is also new from David silver.
The bar switches are new, the reg/rec is new, the fuse holder is new, and the wiring
Harness is new. Any suggestion gratefully received.

It’s not always straight-forward finding an electrical fault/gremlin.  It is never a bad idea to check and clean connections and grounds for all of the other wiring.
Check all wiring to the instrument cluster and gauge lights are clean.

Check and clean connections for turn signals and bulb holders.  Check the signal wiring for shorts.

Make sure all connections are tight.

By the way, do you have any wires anywhere on the bike that are not connected ?  Are any bulbs burned out?


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[scottly]

The last epic thread of an intermittent short turned out to be one of the coil's black primary wire shorting out to the coil mounting bracket. One side of each bracket has a relief to give clearance of the wires, while the other side is flat. The relief needs to face the primary wire on both coils.

[scottly]

Here is a better pic of how the reliefs are orientated to the coils:

[davidp1054]

Thanks Gents,
I will check everything again for tightness and I will remove the coils and re-mount them.
Thanks for the pics.
Cheers

[davidp1054]

Dear all,
I pondered on this issue and could not explain that the bike was running perfectly with no issues when the fuse went.
Scottly sent some pictures of the coil brackets which led me to remove the coils and hang them on their wiresans turn the ignition on, fuse was ok.
I fettled the brackets to relieve them as shown in the photos and wrapped them with insulation tape.
I then refitted the coils to the brackets and to the bike in there original position, turned the ignition on fuse ok. Started the bike and it ran perfectly.
While the bike was running I turned every switch horn etc and then turned the run stop switch, reset the switch to run and started the bike again!!!!!! Amazing. The fault is cured. Thank you so much everyone for all your help, brilliant.

[Robbo]

Glad to hear that you worked it out !!!


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[scottly]

The correct orientation of the coil brackets puts the mounting lugs off-set, which looks wrong. I suspect this is why the brackets are sometimes incorrectly installed?