1980 Honda CB750 DOHC Electrical System Explained 

This is a good video on general electrical troubleshooting of this model. The white plastic block with the alternator wires is referred to as a coupler. It is much better to probe these couplers from the back as it prevents damaging the connecting part of the wire terminal. The starter circuit also includes the neutral light switch so that the engine can be started in neutral without pulling in the clutch lever. I think it used the neutral switch as a ground circuit as well as the clutch lever switch. This model's alternator can generate more then adequate power to keep the battery charged, but with time and use they can get weaker. As well as testing the stator coils, check the rotor for insulation from ground, resistance of the winding and good continuity through the brushes. Since the rotor is always spinning, it can have shorts in the winding that reduce the output. Rotors and stators can be rewound. If the bike is dropped on the left side and the side cover is moved, the stator can rub against the rotor and damage both parts. I don't think testing the open circuit AC voltage from the stator is a valid test. I would rather test the AC voltage between the yellow wires with the engine running and the coupler connected to see if they are similar. You could also test the battery voltage with the engine running, it should be above 12 V and not go over 14.6 V. A long time ago we use to test battery charging amperage, but this test is no longer used much. The ignition on these models is a transistorized system not CDI. The spark units above the battery were notorious for failing. The symptom is that the engine will not rev to red line and the bike acts like it is governed. The coils are probably good, but you may need to cut some of the spark wire off at the plug cap end as the plug caps use a screw that threads into the wire and over time the connections get bad. Peak Voltage testing is the best way to test ignition systems. TecMate has a good tester for this.

That was a wonderful excellent video! I am pretty intimidated when it comes to a bikes electrical system and that was the clearest easiest to understand explanation I have yet to see. Thank you very much!! Btw, love the shirt. Namaste.

This IS one of the best videos of how to work on ANY motorcycle electrical system. Especially custom bikes that need custom wire harnesses. I am an electrician - and I DO suggest that you get a better digital multi meter, and/or NEW tester leads. A 1 ohm reading with just the leads is VERY bad. That will cause volt tests to be wrong - because you are adding resistance into the test. E=IxR (or volts=current x resistance) is Ohm's law. Your leads (or internal meter resistance) is causing bad readings.... Other than that - this is a really great video. I am also glad and impressed that you mentioned in the beginning that electrons flow from negative to positive - just like lightening actually goes from the ground up - lol.. Thanks..

That is one hell of a good video. Lots of details no BS just amazing. Thanks for putting in the hardwork!

I bought a 1980 by the way. It was an excellent video I have a 1980 CB750K when I bought it. The battery was bad, and then the guy hooked up in a car battery to it, but he hooked it up backwards. And before that, all the lights were working on, then after I noticed that he had it on backwards none of the lights would work and then I replaced the 30th fuse. I was born if you knew something else that could have went bad or what could have happened.

Awesome, clear, concise explanation!!! Great video!

Just wanted to thank you for the great work - it is definitely difficult to find good videos on motorcycle maintenance, and if you have a classic bike, much more so. I was gifted a 80s DOHC Honda bike, and you've definitely improved the chances that I will be able to keep and enjoy it, which is how I feel is the best way to thank the person that gave it to me.

Your video saved my life. I work on aircraft avionics and couldn't figure out why the harness in my buddies 80 CB750 wasn't giving any power anywhere. Was especially concerned that it wouldn't activate the starter solenoid. After beating my eyes on the same wiring diagram, and knowing I was right, your video made me 100% sure. Went right back to the battery with a test light, worked my way around, found that I had a loose connection to my ignition and the ground wasn't good for the neutral safety switch. Cranking good, coils got power, and lights work!

You are the first to explain that the whole frame is the earth..back to the battery. For those challenged earths you can use a jumper wire from the negative- side. Although my battery was charged the low V at start up was a key record that the battery was old...2011 it was changed I later found out so 12 years old. I checked my starter to 12v IV it worked, the stop/start switch had continuity so worked. The starter relay was not working correctly. Thx for your help that was excellent.

The signal to noise ratio of this video is extremely high. Everything about this format, delivery, and content is exceptionally thoughtful of the viewer. Much obliged.

For the first time I understood the purpose of each component of the ES on this bike. Thank you very much!

Fantastic video! Really really like your calm and thoughtful approach of describing everything. I mean this in the most positive and complimentary way when I say you’re like the Mr. Rogers of bike mechanics. And the bonus is the comment section of folks adding to the post. I just replaced the reg/rec in my 1981 CB750 Custom with the help of this video. I’ve never worked on bikes before. This is so helpful. Your video gave me the confidence, and it worked!

I learned allot from this video. Thanks for the content!

Fantastic video. Thank you so much for presenting in a clear and thoughtful way. I have 1980 CB750 Custom. A while ago the charging system failed and in troubleshooting I discovered the router was bad. I’m not a “handy” person but enjoy learning and I’m committed to doing all of the maintenance and repair work on my bike. I wish I had seen your video when I was troubleshooting the charging system - would have saved a whole of time! (And to your point on lithium ion batteries - I upgraded when I replaced the router but didn’t realize that I needed a regulator rectifier that worked specifically with lithium ion. That mistake was lesson learned #2!) Thanks again and hope you continue to make more videos.

Another GREAT video! Thanks!

Mr. Masters - I appreciate your review of the CB750 Honda Electrical System. Thanks - I have two 750s. My 79 is fine. The 81 is a Custom for my wife that we just got. Although the turn signals work correctly, The Right Turn Signal ( Blue wire side ) [ will lite up and stay lit if the Running Light ( tail light ) Fuze is okay ] unless used normally as a turn signal. In other words, the Turn Signals work regardless. After about a minute or so, the running light fuse blows, and the right signal side is no longer lit up but is off unless the turn signal is selected. In reviewing the schematic I concluded that the turn signal switch is leaking a positive from the run light brown wire to the blue wire side of the switch. Observations: When the run light fuse blows, the run light does not receive power otherwise. The Turn signal fuse which is adjacent to the Run Light Fuse has not blown - turn signals work normally - Your opinion is most welcomed - thanks !

Good info! Thanks

Well done, thanks!

What a Stud! Thank you!

If you do a complete rebuild then a Motogadgett control box is the way to go. It simplifies wiring hugely.

Thanks 🙏 that’s a great video

excellent ,thank you

Thank you good class.

I have an 82 CB750C- bought with a charging system issue (battery wasn't recharging itself after running for about half an hour). I replaced the battery, rectifier, stator and starter solenoid. Now the bike has no power whatsoever, but I did discover that the 30amp main fuse continues to blow. Any suggestions of where else to look?

A question about your ac stator test...If the regulator applies voltage to the rotor via the black and white wires in order to energize the stator, how do I measure AC stator output without disconnecting the Regulator from the field coil? (they share a connector) Thanks.

Hi will this cover the cb750fn 96 reg .

My cb750 DOHC was having some issues at idle with uneven temperatures on cylinders 1&4 (running hot) and 2&3 (almost 100*F colder). I have a dyna 2000 but what looks like cheap ignition coils. I tested the resistance on the coils and plug caps and they were all wacky. A plug cap on cylinder 4 had a resistance of about 200k ohms. The secondary resistance on both coils was roughly 150k ohms. I’m thinking I need to order some better coils but I also noticed my ignition spark unit melted all the potting out. Could this be caused by the coils being screwed up? Or is there an electrical issue somewhere else that’s causing excess current to the ignition spark unit?

I have a 1979 cb750k it would not charge when I got it I replaced battery stator and the rotor now it will run and charge for about 30 seconds it pops at the rotor and melts one wire off of the rotor and quits charging any ideas anyone

Great video, learned a lot!! I have a 1980 Honda 750f for 43 years now...got it on my 18th birthday..., great bike, but now I am about to give it up.. When I turned the key ALL lit up as usual, and as I tried to start the bike ALL went dark (NO power). I checked the fuses and they are all good, so I tried to test the solenoid and did not spark so I check the battery and it was bad. I replaced with a new solenoid and a new battery and still NO power at all. I decided to get a new ignition and still NO power. The engine does turn when I put the screw driver in the solenoid. I checked the ground connection and I cannot see anything wrong with it. At this point I have no idea what else could be wrong. I really need help

I am having trouble wiring my CDI to a m.unit. I thought I had everything right but my green wire is reading 12v. Do you have any diagrams specifically for the CDI?

Watching your video leads me to believe I have a bad battery. I have a new solenoid and when I try to start the bike my voltage drops to 10 and doesn't come back up. Starter doesn't spin but solenoid clicks

Question, what size relay would I get to get to wire for my led turn signals? And would I just replace whole relay? Thanks in advance!

This is a fantastic video, very helpful. I have the exact bike and I have a problem. The previous owner cut the connector off of the ignition switch and I’m trying to rewire a new plug. I have no idea where what wire goes into what position on the plug. Also it seems the switch has five connections and the plug has six positions, but it seems I have an extra brown/white wire. Can you explain what I should do for this? Thanks!

My rear amber lights are only going on when the turn signal is activated. Is this normal for my 1972 CB750 K. The front amber lights are lit when the headlight goes on but not the rear. All the bulbs are good. What could be causing this?

Hey, thank you for the video it’s a big help. So my 1982 Honda CB650 nighthawk has a charging problem. Before watching your video I replaced the stator and magneto hoping it would fix the issue but it didn’t. After watching your video, when doing the test at time mark 13:24, I found continuity on the black wire. What exactly does this mean and what should I do from here?? I would greatly appreciate the help, thank you.

Donyou happen to have a link to the pdf for the wiring diagram in this video its exact diagram i need for my bike.

do you know what i should look for if my bike keeps blowing fuses when the stater cover is tightened? it will only blow a fuse when it's tight.

Any idea what wire in my head light would cause bike to die when put in gear. Runs fine in neutral. Only thing i did was remove some wiring in head light. I eliminated the left switch and wires low beam direct white and blue wire. Either something there almost like a kick stand safety but doesnt have one 81' or clutch just went..... no clue.

I recently got a 1984 CB700sc nighthawk. When I was riding the bike suddenly shut off and wouldn't start, the only thing that happens is the click from the solenoid. I already checked the new battery and it was good. Do you have any idea as to what the problem is? All the lights come on, and when I bridge the solenoid terminals it doesn't crank as well. Thanks!

This bike does not have CDI but MDI ignition system which is completely different

Just checked everything . All ok, then noticed outside rotor brush worn-out . This brush wears out first because of the difference in circumference and distance it travels over the rotor . Check this first . 5 dollars fo both brushes. Fixed .

I'm not going to skip ahead. So far so good. UPDATE AT THE END OF THIS VIDEO: HOLY crud I'm glad I did watch the entire video. If he didn't break it down i would be lost. Actually i would be shit out of luck if it was an engineer explaining all this crap. Thank you for explaining it the way you did.

Hi just found you channel,,,,can you please send a quick update on why the cdi,s in my bike have melted ,,I have just started to restore the bike and today come across them ,just to say the bike runs ok ,,,thanks Michael from the UK 🇬🇧

I didn't see how to check the diodeps in the rectifier / regulator. Isn't this a common fail issue.

Where is the fusebox located

Does this video pertain to a 1980 cb900C ?

Hi.. Great presentation. What would cause both CDI boxes to cook ..so much so that the epoxy is drained away? Horrendous! The bike is a 79 CB750F. Thanks so much!

What's the function of that generator with the stator

I am become mechanic. I go fast soon.

“Electricity doesn’t see colors”

“I’m not an electrical engineer”