Topic: CB750K4 - new updates 11 Oct 2024 bike not charging - need help!

[andy750]

Thanks Stu me too.

Ok next problem: K2 new harness install getting no spark at #1 and #4 (did not check 2+3) - suspect Dyna S hook up under oil tank as connectors under tank look ok….any other ideas on what to check?

[PeWe]

Andy, check that you can steer max to the right without stretching those wires to brake switch.
I have noticed that they need main harness to sit right on frame, to give needed slack.

When tank is taken off-on these can be affected too.

Another wire causing error is the striped one from rectifier to battery plus cable. An evil bullet plug connection almost hidden behind left side cover, frame tube.

I had to replace the bullet plug to flat type sitting harder. Tricky to see. Mine was corroded causing issues

[newday777]

Thanks Stu me too.

Ok next problem: K2 new harness install getting no spark at #1 and #4 (did not check 2+3) - suspect Dyna S hook up under oil tank as connectors under tank look ok….any other ideas on what to check?

Check the connectors behind the oil tank. You might need to tighten the female barrel connector. That is where the original points plate wire connects as does the Dyna.

[Kevin D]

Andy, this bike has an old harness, yes?
I had a broken wire, intermittent, on the pair that reaches from under the tank to the switch. The copper strands were broken while the jacket was intact.

I replaced the pair from the harness to the switch with some super flex meter lead wire and no more broken wires.
Oh, I have had to squeeze the barrels a time or two so there’s a good contact at the male-female switch connection.

[andy750]

Ok thank you for all the input very much appreciated. The K2 now runs but there are a few curiosities....

1. Kevin - its a brand new harness (after last one melted at rectifier)
2. I have  attached photos of the left and right switches (bought of Ebay 20 years ago unsure of CB750 year)
3. The right hand switch -engine kill switch has never worked
4. Dyna S connections under oil tank/fuel tank all good.
5. The right hand switch has two black wires and a black/white wire coming from it in the headlight bucket
6. When black is attached to black and black/white connected to black/white connector the starter cranks over but there is no spark
7. When black/white from right hand switch is connected to black female from right hand switch...and black male from right hand switch connects to 4-way black connector from harness then there is spark and bike runs and idles just fine -I dont understand this...and headlight is no longer working 

So bike runs but something is off and headlight is not working no matter what I do - I recall that even in old harness that I always had the black/white wire looped into black female connector as this is how bike ran. I never questioned it before as it worked though I couldnt explain it. Just not sure now why headlight is not working - I changed the bulb and thats not it.

K2 only has one fuse so not a lot of wiring in headlight bucket - unlike the K4. A but stumped for the time being. Off to troubleshoot but looking forward to your opinions on why the bike is running with this configuration. Photos attached to go along with the explanation.

thanks
Andy

[newday777]

Andy
It looks like you have K3/K4 switches not K2.
K2 will have headlight on right side of Off-Low-High and will have different wiring.

[newday777]

K2 left switch is special.

[PeWe]

Good idea to check all functions on switches before connecting them. Mark on tape on wires close to connector.
- A buzzer makes it easier.

Your LH switch look almost as K6 switch. Compare with Honda diagrams.

K6, K7 diagrams show a jumper wire between Br/wh -Bk. Not on a new harness.
Switch model might be involved here.

[andy750]

Thanks for identifying the year of my switches - have been using them for years with no issue just cant recall how the wires hook up  . Ill need to unplug and start again. Per thanks for the note about the brown/white-blck jumper I do have a loose br/w. Thanks Stu for the very clear photos of what makes the K2 special

[andy750]

Solved!!! Headlight and all lights working and bike starts up!! Success!!

Ok solution was:
1. K3-K5 switches (RH and LH)
2. RH switch: b/w connects to black
3. RH switch: 2nd black connects to 4-way black/harness
4. RH switch: brown/white connects to 4-way brown/white harness

Headlight to work:
1. Blue headlight wire to 3/4-way blue harness connector
2. White headlight  wire to white LH switch
3. Green headlight to green 4-way harness connector
and finally the puzzle piece….
4. Brown/red LH switch to single brown connector/harness!!
Wires with no use in my K2
LH switch: brown/white, brown/blue, orange/white, blue/white
These are for clutch safety switch and buzzer I think.
No test ride yet as too dark tonight but that comes next

[newday777]

That's great you got it solved and running and ready for a ride.

[PeWe]

Good news Andy.
It feels nice when riding when you know the bike will not suddenly stop.

[andy750]

Yes it does feel good to know that everything is working.

One last question on the K2: last time I installed a new wiring harness on the K2 it melted after 150 miles at the main fuse area. Since then I have installed another new harness, new battery, got a new main fuse setup from Yamiya and a new recitifier also from Yamiya.

What tests can I do to make sure everything is working as it should be and not overcharging? Little paranoid now 

[PeWe]

When I had installed all electrical stuff on my K2 I measured the current.
Plus cable not connected on battery. Auto multimeter 20A setting, measured between battery and plus cable. Thick clamps needed that can handle a few A.
It should not flow any current when ign switch is off.
Minus side works too.

Just subtract all loads in W and   /12V.
No need to use starter

Switch on headlight on, killswitch on.
Saw everything was OK.

Remember to connect probes back to V measuring connectors on multimeter.
Easy to blow fuses otherwise when measure V on specific circuits 
I hope I have done that mistake for the last time!!

[andy750]

Thanks Per appreciate the detailed write up. I want to be as sure as i can possibly can that I wont be melting any more wires 

[Kevin D]

Yes it does feel good to know that everything is working.

Yay!

[andy750]

First ride out with the barn door fairing - good for chilly Spring rides and will no doubt soon be removed as it’s quite ugly the modern setup with TPMS monitor (have it on my Tenere T700 and love it) - had over 8 punctures on this K4 , the voltage monitor doubling as a charging port, the Rockford iPhone holder - overall so functional! Good for touring


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[andy750]

The LED taillight is good for city driving in Boston.


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[newday777]

I have thought about putting one of the Vetter fairings I have on my K5 last week for the chilly spring rides. I was out enjoying the one on my friend's K4 that I finished working on a couple weeks ago and test rode it 60 miles each way over to the Maine border and back. It made 50° seem 10° warmer.

[andy750]

I have to say Stu those Vetter fairing do look attractive at this time of year. 60 miles each way is very good going for right now!

[newday777]

I have to say Stu those Vetter fairing do look attractive at this time of year. 60 miles each way is very good going for right now!

Last weekend I rode my K5 70 miles with it starting out at 55° and finishing at 57° without a windshield. A little nippy but very doable.

[andy750]

I have to say Stu those Vetter fairing do look attractive at this time of year. 60 miles each way is very good going for right now!

Last weekend I rode my K5 70 miles with it starting out at 55° and finishing at 57° without a windshield. A little nippy but very doable.

I used to ride to work (4 miles each way) on my K4 (no fairing) when it was 15F 

[andy750]

All summer the K4 has been running great and I went on camping trips, road trips etc…now at the best time of year - Fall - the bike is not charging 🥲. I have a volt meter installed at handlebars so I can check battery…reads 12.0v while riding and slowly decreases on short test loop.

So far…
1. New battery - no difference
2. Working battery from K2 - no difference.

So it’s not the battery

Trouble is I have an aftermarket rectifier/alternator - one of the famed alternator upgrades bought from a forum member (Anders) years ago - been working great as well for thousands of miles. But….how to troubleshoot!? Not sure on where to start with this and keep in mind I’m electrically challenged (though did fix the VStrom charging issue myself - reglueing alternator magnets ).

Any advice on where to start would be great

Thanks
Andy



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[newday777]

Well darn it Andy!
Did you contact Anders yet to see what he would advise?

Sean had an aftermarket reg/rectifier go out, again not long ago.

[andy750]

hey Stu thanks for chiming in. Anders does not respond to my emails so thats out. I guess Ill need to dismantle and check. I was hoping there was some electrical test I could do to verfify which part has failed.