Author Topic: black wire on voltage regulator 1976 CB750  (Read 535 times)

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Offline davidp1054

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black wire on voltage regulator 1976 CB750
« on: October 23, 2018, 05:44:45 am »
Help!!!
I am looking to replace my regulator but when I pulled of the wires of the old one and metered them out both the green wire and the black wire are ground and connected to each other.
Can anyone advise if this is correct! I am not sure but don't think the ground should be connected to the power.
The black wire is connected to the ignition switch, brake switch, warning lights etc.

Offline calj737

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Re: black wire on voltage regulator 1976 CB750
« Reply #1 on: October 23, 2018, 05:54:13 am »
Black for the Regulator is the 12v sensing wire. Green is ground. They should not "connect".

From your key switch, Black is switched 12v providing power to instrument cluster, brake switches and ignition.

Why are you choosing to replace the Regulator?
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Offline davidp1054

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Re: black wire on voltage regulator 1976 CB750
« Reply #2 on: October 23, 2018, 07:53:12 am »
bike was running great but on increasing revs the bike miss fired and stopped. Main fuse was blown.
I replaced the fused and tried to start the bike, lights worked starter worked bike was not starting as there was no spark. I disconnected the stator and checked the yellow wires, that was ok, checked the rectifier that was US, checked the regulator, that was bad, totally grounded,, checked the whit wire to green for continuity there was no connection but when I checked the black wire to the green wire they were connected.
I haven't got a clue what has happened but am assuming maybe a wire has melted together in the harness.
I have continuity checked the black wire and it is connected to all the points it should be.
Any suggestions?

Offline calj737

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Re: black wire on voltage regulator 1976 CB750
« Reply #3 on: October 23, 2018, 08:04:54 am »
A blown MAIN fuse and BLACK finding continuity to ground tells me yuor Black wire within the harness has shorted out. This wire also serves the RH bar controls for KILL, becomes BLK/WHT to coils with RUN. Since you had the issue, then no spark, that would lead me to investigate the KILL switch wiring and the coil wire (power side).

It is not unusual for a wire to fray behind the headlight and underneath the bars. If the Black does, it’s giong to short out promptly. With that wire damaged, the Reg/Rec functions will be totally askew.

With the Black disconnected from Reg, do you get continuity to ground anywhere on the bike? To the battery NEG, motor bolts, frame screw? Also, with the key OFF, test this with RUN set to on.
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Offline davidp1054

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Re: black wire on voltage regulator 1976 CB750
« Reply #4 on: October 23, 2018, 08:38:49 am »
yes, I get continuity between black wire and chassis anywhere with the ignition key on and off and also the run switch on and off

Offline calj737

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Re: black wire on voltage regulator 1976 CB750
« Reply #5 on: October 23, 2018, 09:04:16 am »
There's your problem. Start tracing it from the KEY to the cluster, the handlebar, and the coils. Somewhere its shorted out.
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Offline davidp1054

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Re: black wire on voltage regulator 1976 CB750
« Reply #6 on: October 23, 2018, 09:14:33 am »
Thanks Calj737,
You have confirmed exactly what I was thinking but I did not have the electrically knowledge or confidence to
confirm.
Thanks I will start tomorrow

Offline scottly

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Re: black wire on voltage regulator 1976 CB750
« Reply #7 on: October 23, 2018, 09:51:22 am »
There WILL be continuity from the black wire to ground from the loads attached to the black wire that are energized when the key is on! A simple continuity test is not valid. If the black wire were shorted to ground, the new fuse would have blown as soon as the key was turned on.
Don't fix it if it ain't broke!
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Offline Spanner 1

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Re: black wire on voltage regulator 1976 CB750
« Reply #8 on: October 23, 2018, 07:20:49 pm »
Scottly+1. With the key 'off' and a meter ( set on ohms scale ), there will be continuity between Black and Ground. Normal, 'cos the coils are in circuit , so not a valid test. Nothing wrong with your stator, regulator or rectifier, just a #$%*ty fuse block for starters ! If you can pull the fuses out with your fingers then the fuse block = no good . Try shining up the fuse clips and ( I mean shiny ) then carefully bend the clips together so as they get a solid grip on each fuse. This work alone may fix your problem IMO. good luck !
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Offline davidp1054

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Re: black wire on voltage regulator 1976 CB750
« Reply #9 on: October 24, 2018, 07:24:06 am »
I have checked and found that he brown and white wire in the headlight is connected to black which is correct to the wiring diagram I have for a 1976 model. When I pull the brown and white wire the black is no longer connected to ground.
I have seen other wiring diagrams which don't have the brown and white wire connected to the black! What do I do? Which one is correct?

Offline bryanj

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Re: black wire on voltage regulator 1976 CB750
« Reply #10 on: October 24, 2018, 02:12:03 pm »
Does the brown/white go to instrument or rear light? If so there will be a low resistance but not a short through the bulb
Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

Remember "Its always in the last place you look" COURSE IT IS YOU STOP LOOKIN THEN!

Offline scottly

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Re: black wire on voltage regulator 1976 CB750
« Reply #11 on: October 24, 2018, 07:01:52 pm »
bike was running great but on increasing revs the bike miss fired and stopped. Main fuse was blown.
I replaced the fused and tried to start the bike, lights worked starter worked bike was not starting as there was no spark.
Let's fix your problem of no spark, instead of chasing imaginary gremlins. ;)
First question: how did you check for spark?
Don't fix it if it ain't broke!
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Offline davidp1054

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Re: black wire on voltage regulator 1976 CB750
« Reply #12 on: October 25, 2018, 12:35:37 pm »
Gents,
I have a brown and red wire off behind the fuse box which could have caused the fuse to blow.
I have put the wire back now and cleaned and bent the fuse holders together to provide a good connection. I have checked the coils and only have 1ohm resistance primary coil and the spec is 4.7 ohms.
I have fitted new coils of the correct spec 4.7 ohms primary and 14000 ohms secondary.
I am now fitting a new reg/rec as the regulator was u/s.
stator tests ok to the Honda manual spec so I will check spark when I have completed works.
The advise has been invaluable the bike would have been stripped without it,  Many Thanks
I will post the results.

Offline davidp1054

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Re: black wire on voltage regulator 1976 CB750
« Reply #13 on: November 02, 2018, 02:14:42 pm »
OK, to recap,
I have now fitted a new wiring harness, a new fuse box, a new ignition switch, a new all in one regulator rectifier, and a new pair of ignition coils. (Didn't want to waste time on testing the loom.)
I have completed the static tests on the stator, there are no shorted turns/down to grounds and I get the correct readings as per every 3 phase test I have instructions for and on u tube.
I completed the fitting and the wiring to the sohc/4 1976 cb750 wiring diagram.
Turn on ignition switch and the 15 amp fuse blows instantly in the middle every time, as before.
The bike is exactly as it was when it was running a week a go and stopped except all parts are new.
This looks like something is shorted out but I don't have a clue now what it could be.
The only niggle or non understanding I have is that the wiring diagram shows the brown/white wire connected to the black wires, however that is how it was when it was running before so I am assuming the diagram is correct. Does
anyone have any ideas or other tests I can carry out?
my battery is at 12.6 volts at the moment.

Offline 69cb750

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Re: black wire on voltage regulator 1976 CB750
« Reply #14 on: November 02, 2018, 05:37:30 pm »
Quote
This looks like something is shorted out but I don't have a clue now what it could be.
Yes

Quote
The only niggle or non understanding I have is that the wiring diagram shows the brown/white wire connected to the black wires.
The brown/white wire is for the tach and speedo lights.
You can turn the headlight off on the early bikes, later bikes headlight is always on.

Quote
Does anyone have any ideas or other tests I can carry out?
Disconnect everything from harness except ignition and fuse, leave switch on, connect one wire and check fuse, repeat, when fuse blows you have found the short.

Offline davidp1054

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Re: black wire on voltage regulator 1976 CB750
« Reply #15 on: November 03, 2018, 07:49:30 am »
Thanks  69cb750,
I found the wire that shorts everything out, see photo.
This is the right handle bar switch which is the starter button and the run stop switch.
There are 5 wires, two blacks, one black an.d white, one black and red and a yellow and red. Each wire is attached to the correct colour as per wiring diagram, the two blacks are connected together.
When I remove the black shown the fuse is ok and everything works as it should, but I have not checked spark yet.
This is a new switch from David Silvers. when I pull all the wire from the switch there are no shorts wire to wire or down to ground but the black wire causing the problem seems to be connected to the black and white wire, I am assuming that these are the two wires connected to the run switch. Do I connect this black to the black and white wire? because when I attach it to the black wires as per wiring schedule it blows the fuse?  any ideas or suggestions


Offline bryanj

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Re: black wire on voltage regulator 1976 CB750
« Reply #16 on: November 03, 2018, 09:18:58 am »
That means that there is either a short on the black white to coils or there has to be a short in the switch
Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

Remember "Its always in the last place you look" COURSE IT IS YOU STOP LOOKIN THEN!

Offline TwoTired

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Re: black wire on voltage regulator 1976 CB750
« Reply #17 on: November 03, 2018, 09:33:52 am »
To aid in the trackdown of finding the branch that causes the short, and where it is actually shorted without spending a fortune on fuses...
Clip a 12v lamp in place of the fuse and activate the circuit.  The lamp will limit the current flow to safe levels, and likely shine brightly.  It will dim when the short has been removed, makeing it safe for fuse installation.

Step one, find the branch.  Step two, inspect and probe along the branch to find the short.  Don't overlook what the branch ultimately connects to ( bulb/ socket or whatever) may have shorted instead of being a simple resistive load resistive.

Cheers,
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Thinking:  It's like reading with your own mind

Offline davidp1054

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Re: black wire on voltage regulator 1976 CB750
« Reply #18 on: November 03, 2018, 01:33:02 pm »
Thanks fior the suggestion folks I will fit a lamp and carry on. I hope its not
The new switch!

Offline davidp1054

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Re: black wire on voltage regulator 1976 CB750
« Reply #19 on: November 04, 2018, 09:22:44 am »
Chasing my tale here, removed the black starter switch wire fitted a new fuse and everything worked except no spark.
Put the black wire back into the loom and disconnected the black and white wires from the coils, fuse blows.
Put the black and white wires back into loom and removed the black wire from the reg/rectifier, everything worked and with a spark. Grounded the reg/rec and put the black wire into the loom everything worked with spark. Started the bike but main fuse blew!!!!!?
Any ideas?


Offline 69cb750

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Re: black wire on voltage regulator 1976 CB750
« Reply #20 on: November 04, 2018, 10:55:09 am »
Quote
Any ideas?
Run wire from positive battery terminal to coil leads, start and ride bike one mile.
Original coils or new coils ?
The primary (inside coil) could be shorted and drawing enough to blow fuse.

Offline davidp1054

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Re: black wire on voltage regulator 1976 CB750
« Reply #21 on: November 04, 2018, 11:25:45 am »
Do I connect the live wire to the black and white wire.
I assume I don't need the ignition switched on.
The new coils are fitted!

Offline Robbo

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black wire on voltage regulator 1976 CB750
« Reply #22 on: November 04, 2018, 11:47:45 am »
That’s a bandaid solution of some sorts???  I wouldn’t do that.

Find the real issue and fix it properly.

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Offline TwoTired

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Re: black wire on voltage regulator 1976 CB750
« Reply #23 on: November 04, 2018, 08:47:26 pm »
Do you have and are you using a wire diagram appropriate for your bike?

Cheers,
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Thinking:  It's like reading with your own mind

Offline davidp1054

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Re: black wire on voltage regulator 1976 CB750
« Reply #24 on: November 05, 2018, 09:10:53 am »
Yes I have the 1976 diagram downloaded from this site

 

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