Cb750 -71 electrical wiring question

Cb750 -71 electrical wiring question

diggidan
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diggidan
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Joined: March 16th, 2018, 9:17 am

March 16th, 2018, 9:18 am #1

Hi guys!

I have a cb750 from 1971 and I'm going to change out the rectifier and regulator to one combined thingamagig. I don't have any electrical scheme of the new box.

Now the problem is that the colors of the new box dont correspond to the colors coming out of the engine.

From the engine I have the colors:

3 Yellow

White

Green

Light green / red

Blue / red

And in the box has:

3 Yellow

Red

Green

And out from the box comes:

Black

White

I know that the LG/R and B/R is neutral and oil from the engine.

And the yellow ones are quite self explanatory but the question is:

Do I connect the green from the engine with the green on the box? As far as I can understand the green is earth from the alternator?

And do I connect the white from the engine to the red on the box?

I have gone through the electrical scheme but I can't figure out what the white from the engine is...

Very thankful for any insights!

Skickat från min LG-H870 via Tapatalk

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CHUCK DV
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Joined: April 9th, 2003, 9:46 pm

March 16th, 2018, 2:37 pm #2

What brand thingamagig do you have ???
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diggidan
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diggidan
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March 16th, 2018, 6:29 pm #3

CHUCK DV wrote:What brand thingamagig do you have ???
That's "ebays finest noname brand"!
I have contacted the German seller and asked for a diagram so we'll see if he gets back to me.
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CHUCK DV
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Joined: April 9th, 2003, 9:46 pm

March 16th, 2018, 9:31 pm #4

Pic please..or e bay # so we can see it
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diggidan
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diggidan
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March 16th, 2018, 9:44 pm #5

CHUCK DV wrote:Pic please..or e bay # so we can see it
Ebay number is:
#332383666439

Thanks! :)
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CHUCK DV
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Joined: April 9th, 2003, 9:46 pm

March 17th, 2018, 11:15 pm #6

Some Reg/rec  have 8 wires   the  bundle of 2 wires (white and black) the black goes to ground and the other bundle 6 (3 yellow/red/black/green)the black goes to hot key on.
Here is I pic of 8 wire one . If it is a 7 wire it will only have one black that goes to hot when key is on 
39973228385_07217e0654_o.jpg
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itheo58
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itheo58
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Joined: June 17th, 2014, 3:32 am

April 6th, 2018, 2:55 am #7

Hi .If you purchased on Ebay make sure reg/rectifier is for a cb 750 Ki-4 and not later models.
I got caught out as they have exactly the same wire colour but later type will not work on the sohc.
I was in a hurry when my previous brand new unit got ruined because the eth wire broke of from frame.
This Unit was from Tommy but US post being so slow to Oz purchased one from a local Vintage supplier that had in stock [electrix ] but cant remember what model
Ended up getting another from Tommy that  was identical.
Wires are 3 yellow from alternator
Green to eth
Red to battery
Black from Ignition .
To be on the safe side I have bonded wire to eth on frame with another to the Battery should it come off the frame as became an expensive repair.
New Battery was ruined ,one coil melted ,one new regulator of no use as could not be resold and to top it off warped my head as rode home on 2 cylinders for an hr as bike was too long for a trailer and thought would be ok.
One benefit was discovered that a valve seat was loose and could of destroyed a new motor. was advised that would be cheaper to find an alternate head
was able to purchase another head for $100 AUS that was port and polished but modified to resemble a K1 head and had no other bidders .
Cost me $300 to have valves matched and a few helicoils inserted .
At the time of writing the head is now fitted and ready to set valve timing so should soon have back on the road .
you may also want to consider a Volt meter as I thought my regulator was ok as headlight went brighter when revs built up so thought the regulator had not been damaged. 
ended up pumping 17 volts at fast run.
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itheo58
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itheo58
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Joined: June 17th, 2014, 3:32 am

April 7th, 2018, 5:37 am #8

itheo58 wrote: Hi .If you purchased on Ebay make sure reg/rectifier is for a cb 750 Ki-4 and not later models.
I got caught out as they have exactly the same wire colour but later type will not work on the sohc.
I was in a hurry when my previous brand new unit got ruined because the eth wire broke of from frame.
This Unit was from Tommy but US post being so slow to Oz purchased one from a local Vintage supplier that had in stock [electrix ] but cant remember what model
Ended up getting another from Tommy that  was identical.
Wires are 3 yellow from alternator
Green to eth
Red to battery
Black from Ignition .
To be on the safe side I have bonded wire to eth on frame with another to the Battery should it come off the frame as became an expensive repair.
New Battery was ruined ,one coil melted ,one new regulator of no use as could not be resold and to top it off warped my head as rode home on 2 cylinders for an hr as bike was too long for a trailer and thought would be ok.
One benefit was discovered that a valve seat was loose and could of destroyed a new motor. was advised that would be cheaper to find an alternate head
was able to purchase another head for $100 AUS that was port and polished but modified to resemble a K1 head and had no other bidders .
Cost me $300 to have valves matched and a few helicoils inserted .
At the time of writing the head is now fitted and ready to set valve timing so should soon have back on the road .
you may also want to consider a Volt meter as I thought my regulator was ok as headlight went brighter when revs built up so thought the regulator had not been damaged. 
ended up pumping 17 volts at fast run.
Forgot about the white wire which feeds into alternator.
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Shovelpan69
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Shovelpan69
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Joined: September 5th, 2016, 3:29 am

April 16th, 2018, 12:17 pm #9

Has this issue been solved? If not pm me and I'll send you what I have
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diggidan
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diggidan
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Joined: March 16th, 2018, 9:17 am

April 16th, 2018, 1:58 pm #10

Shovelpan69 wrote:Has this issue been solved? If not pm me and I'll send you what I have
Unfortenatly no, I think I have decided to wire the old stuff back on the bike...
Mostly because I'm super afraid of burning the bike. I want to fix the new stuff but I don't know if it's worth the risk.
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