Topic: 1975 honda cb750 wiring

[weltzing]

hi all i have a 75' cb750 and on the clutch handle there are two wires coming from it. these to me look like a clutch safety like cant be started without clutch pulled in. anyway these two wires go to the headlight and my questiong is what do they plug into?? ive tried different things and blow the main fuse. then on the other handle there are like 5 wires coming from the right handle bar switches, i have them all plugged in correctly except for the green wire, i believe its for the starter button because it doesnt work now as it did b4 i messed around with the wires. please help!

[scottly]

The solid green wire from the clutch sw goes to a solid green wire on the harness. The green/red(?) wire goes to a junction with two other like-colored wires.

[1080]

 weltzing 
Looking at the schematic, the green goes to ground & the green/red goes to a starter button green/red wire which goes to a starting motor safety unit. The safety unit is located with the fuse holder & turn signal relay area.

[Popwood]

Yes, study your wiring diagram. You can get a nice color coded one at oldmanhonda.com as well as some other cool stuff. The diagrams in the manuals always seem to be fuzzy and just black ink so not very helpful. The actual color one I reference are a godsend.

[weltzing]

ok i could have sworn that i had the gree hooked up to the harness with all green wires, then had both the red/green wires hooked up to the single red/green wire leading to the safety starter thing. but yet i blow the main fuse and the starter button would still not work.

[1080]

If your main fuse blows, check your rectifier. If it only blows because you hook up the clutch switch then check for proper switch function ( check with ohm meter ) ,but the switch should not be the cause of the fuse to blow, sounds like the safety unit may be at fault?

[1080]

Here's the manuals schematic of the safety unit, hope this helps.

[nobody]

http://www.cmsnl.com/classic-honda-fansite/honda_wiring_diagrams/CB750(K3-K7).jpg

[weltzing]

thanks for all the help! but i found out what it was, i had all the wiring right, i found out that one of the lights on the handle bars for the oil light came out of the holder and was touching the frame which grounded it....

[lucky]

What would be very helpful is a 1975 wiring diagram that does away with the starter motor safety unit since you cannot buy one.
Also a 1975 wiring diagram that incorporates a modern Regulator/rectifier .

And also what to do with the yellow wire with red stripe coming from the starter solenoid and the green with red stripe wire.

And last where does the red wire and r/w with that two prong plug go to?

You can buy a brand new 1975 wiring harness which is helpful but there are still loose ends.

Why can't the people that make these diagrams and modification parts get it right!

Just ONE good 1975 wiring diagram.  Thats all.

Even the wiring diagram in the Honda shop manual is wrong ,and incomplete.

[Patrick]

It is easy to bypass the safety unit. There are two wires into the starter solenoid. On pre-76 750s one wire is a ground and runs to the starter button. The other wire is the hot wire. the safety unit makes the hot wire pass a couple of tests before it will provide juice to the solenoid. You can wire around it by leaving the starter button wire (R/Y) alone and running a connection from a black wire (hot wire on with the key) to the second wire on the solenoid. You could also connect to the red wire to the ignition, but then your solenoid would be always on and drain your battery.

On 77-78 750s they polarization to the solenoid is reversed and the starter button is the hot wire. The safety system on those bikes makes the second wire - the ground wire - pass a couple of tests before it will provide a ground to the solenoid. Leave the starter button wire alone and run a ground wire to the second wire.

Patrick

[lucky]

Patrick you now have me totally confused.
Please do not tell me what does NOT work. It just confuses everything.

It seems like when forum members explain something it is much more confusing.
"On pre-76 750s one wire is a ground and runs to the starter button."
Are you talking about that wire from of the wiring harness? Or is it the one coming from the solenoid? Or is it the one coming out the front of the wiring harness up in the front of the bike?
Does the Green wire connect to a green wire from the harness in the area of the solenoid?

"The other wire is the hot wire."
Your words.
 Hot wire to what? Do you mean the yellow wire with the red stripe? Does it connect to a yellow wire with red stripe coming out of the wiring harness? If so both ends,the one from the solenoid AND the one from the wiring harness both have male connectors. The wiring harness is new and the solenoid is original.

I am using a stock wiring harness that has been remanufactured and looks like the OEM part.
I am not wiring it from scratch.

[lucky]

Look at that wiring schematic above. Many of the wires do not even have the color marked on either end of the wire. See what I mean.
Just more confusion all over the place.

[lucky]

Patrick, Can you tell us how to bypass the starter motor safety unit on a 1975 version of the CB750?

[lucky]

What is really needed is a wiring diagram for a 1975 CB750 that has a modern rectifier/regulator unit.

Someone makes the Rectifier /regulator unit and sells it and then the owners/forum members-motorcyclists have to fix all the problems with what we do with the rear brake light switch and other items that use to hook up to the regulator.ETC.

The people wiring from scratch have lots of wiring diagrams to choose from.
But many of those DO NOT include a version with a modern regulator/rectifier unit.

[andrewk]

Modern regulator/rectifier is easy.  You've got the stator wires, keyed 12v, fused 12v (Batt +), field, and ground.  IMO, a diagram specifically for it is not needed, as there are 3000 "how-to's" on solid state charging.

The rear brake switch isn't so much wired to the regulator as it is to a keyed 12v source.  They share a common splice, (at least according to the diagram) but changing the regulator/rectifier doesn't disable the brake switch, unless you physically remove the wire going to it.  The diagram merely signifies that they share the same 12v circuit.  It's easy to get lost in the wiring diagram, but it's easier to see this once you are looking at the harness.

Making the safety unit go away isn't that difficult either.  You need to unhook the red/yellow from the safety unit and put it to ground.  The black wire of the solenoid has keyed 12V, the starter button completes the ground to make the solenoid pull in.

A specific wiring diagram isn't really needed for any of these modifications- just a proper understanding of DC and how these components work.  I find that for little "custom" projects like this, it's best to have a factory diagram to use as a guide, rather than as an "end all be all."

Best of luck,
Andrew

[Rigid]

Lucky needs more education regarding electrical terminology and basic wiring techniques, and fewer ideas about what others need to do.  IMHO.

[lucky]

Modern regulator/rectifier is easy.  You've got the stator wires, keyed 12v, fused 12v (Batt +), field, and ground.  IMO, a diagram specifically for it is not needed, as there are 3000 "how-to's" on solid state charging.

The rear brake switch isn't so much wired to the regulator as it is to a keyed 12v source.  They share a common splice, (at least according to the diagram) but changing the regulator/rectifier doesn't disable the brake switch, unless you physically remove the wire going to it.  The diagram merely signifies that they share the same 12v circuit.  It's easy to get lost in the wiring diagram, but it's easier to see this once you are looking at the harness.

Making the safety unit go away isn't that difficult either.  You need to unhook the red/yellow from the safety unit and put it to ground.  The black wire of the solenoid has keyed 12V, the starter button completes the ground to make the solenoid pull in.

A specific wiring diagram isn't really needed for any of these modifications- just a proper understanding of DC and how these components work.  I find that for little "custom" projects like this, it's best to have a factory diagram to use as a guide, rather than as an "end all be all."

Best of luck,
Andrew

Thanks for the help.
Your explanation you say
    "Making the safety unit go away isn't that difficult either.  You need to unhook the red/yellow from the safety unit and put it to ground.  The black wire of the solenoid has keyed 12V, the starter button completes the ground to make the solenoid pull in."


Does this mean that since you say to "unhook the y/R wire from the safety unit and put it to ground that the safety unit is still in place? OR just take it off of the bike?


Or do you mean REMOVE the safety unit from the bike, and the take the plug from the wiring harness that was used to plug the safety unit into and put that Y/R wire to ground?

[Patrick]

There are two wires that come out of the starter solenoid. The R/Y wire goes to your starter button and provides the ground for the starter circuit. Leave it alone. The color of the second wire that comes out of the solenoid changed over the years, so I don't remember what color it was in '75. But that second wire is the positive for the starter circuit. Connect it to a black wire. If there isn't a black wire close, then run a wire to a black wire somewhere. This completes your starter button circuit and will allow the starter button to turn the starter. You can then remove the safety unit from your bike if you want because it no longer serves a purpose.

Patrick

[lucky]

There are two wires that come out of the starter solenoid. The R/Y wire goes to your starter button and provides the ground for the starter circuit. Leave it alone. The color of the second wire that comes out of the solenoid changed over the years, so I don't remember what color it was in '75. But that second wire is the positive for the starter circuit. Connect it to a black wire. If there isn't a black wire close, then run a wire to a black wire somewhere. This completes your starter button circuit and will allow the starter button to turn the starter. You can then remove the safety unit from your bike if you want because it no longer serves a purpose.

Patrick

You are right Patrick.

I just bought a brand new 1975 starter solenoid and it has a yellow/R wire and a Green/R wire coming from it.

It was obvious that the yellow/R wire plugged into the yellow red wire from the harness. But there was no Green /R red wire from the harness to plug into the green /R wire coming from the starter solenoid.
But there was a black wire coming from the harness with the yellow/R wire from the harness so I just figured that the green/R  wire from the solenoid should go to the black wire from the harness.

The wiring diagram for the 1975 model shows a black wire to the solenoid.

What I do not understand is that I bought a 1975 solenoid and a 1975 harness and there should be no problems.
But one wire was green/R and the connectors were both male instead of female.

I wish they could get this stuff right.
The same company  sells the harness and the solenoid.
You would think they would just look the solenoid and harness at it and see if it works.

I guess I am dreaming...Just buy all new parts and they all plug in. LOL

Matter of fact the 1978 model is the only one that has yellow/R and green/R.
All the earlier models use the yellow/R and black wire coming from the solenoid.

Maybe I was sold the wrong part.

[Patrick]

That is a solenoid from a 77-78. It works exact like the earlier models, but the polarity is opposite. I sorta doubt, though, that polarity is important. I think the switch works whichever way you hook it up. It's just a  switch, not a diode.

On the later models the r/y wire is positive and it goes to the starter button. Inside the right hand handlebar switch the starter button transfers power from the headlight to the solenoid when you press the starter button. The headlight goes out until you release the starter button, then the power is transferred back to the light.

Likewise, the second wire from the solenoid is ground. The bikes with the early safety system required the electrical system to pass one of two tests (bike in neutral or clutch pulled in) before it would supply power to the solenoid. The 77-78 makes the system pass the same test, but it withholds the ground until those tests are passed. So with a 77-78 (and maybe 76) I would have told you to leave the starter button wire alone, but the run the second wire to either ground or a green ground wire.

It is really a simple system. They just make it LOOK complicated.

Try hooking the solenoid up with the connectors properly aligned and ignore the color of the wires. I would like to know if that works. I never tried it that way.

Patrick

[lucky]

I appreciate al of the help.

It turns out that the correct solenoid for the 1975 model is no longer sold so I just used the one they gave me and plugged it in even though the colors of the wires are not correct.

Anyway it all works now as it should.
All that is left is the turn signals and I have no problems with that.

Thanks for everyone's input. I appreciate it. It all helps.

All of this plugs right into the 1978 harness from the alternator.

Other than the solenoid it was all plug and play.
1975 OEM style harness.
Ricks' Motorsports regulator/ rectifier.
1975 OEM style Emglo ignition switch.
I got a new engine harness from Yamiya, Japan.
Stock 1975 OEM style Fuse box (NEW)

Got rid of the SMSU. Looks like trouble later on.