Topic: Uh Oh, Broken it: Electrical

[M 750K6]

CB750K6. Pulled it out this morning. Ignition on, both oil and neutral light, as normal. Started it up. All fine. Then plugged in my heated jacket. It died and no lights anywhere, no starter.

Thought I must have blown a fuse. All 3 look good and have continuity across them with my meter. I have 13v on the battery and:-
1. 12.9v  to either side of the fuse holder;
2. 12.9v to the plug connecting the key switch.
So, I'm thinking I have continuity to that point. On the key switch plug 3 terminals are 12.9v to the positive battery terminal and one is 12.9v to the negative battery terminal. I looked into the headlight birds nest. Everything looks to be connected.

So, I need to go through this methodically, to find where I first start to lose power. Can anyone point me to the best approach? I have a K4 wiring diagram that is clear enough to see the colour coding info. I have no real prior experience with m/c electrical gremlins. In the past I've only ever labelled and photographed everything when dismantling and put it back in the same order, without knowing what I'm touching!

Thanks 👍

[MauiK3]

Where was your jacket connected?

[M 750K6]

A separate fused lead, direct on the battery terminals. It has worked for me before on this bike, without problems.

[M 750K6]

I've been studying the wiring diagram. I think I'd like to test that the keys witch is working. What is the best way to test that, please?

[Don R]

 I've seen a bad battery act like that, they show voltage but as soon as you add a load nothing is there. If you can load test the battery, try that before you go crazy checking things that are working. My second guess would be the key switch.

[M 750K6]

I think the battery is OK. It started the bike without labouring. It's back on my smart charger. I'll check it tomorrow.

I have given up, for today. I have found the sidelight comes on, when I turn the ignition key to position 2. So that's working. Any suggestions on how to check whether the key switch is passing power through at position 1, so I can rule the switch out?

[seanbarney41]

So crazy...literally just finished up with this exact problem on a k4 I have just put back together, only no heated gear...mine is for sure the key switch...first it did not work, started tracing the problem, started working before I found the problem, thought it was fixed, then stopped working next try after everything back together.

Just unplug the key switch and at the square 4 pin with the key on should have continuity between red and black, and continuity between brown and brown/white.  No continuity with key off.

 tried to take the switch apart and repair but the backing plate did not survive crimping the case closed again.

[M 750K6]

Perfect. Will give that a try. 👍
P.s. sorry your switch didn't make it.

[bryanj]

Red is 12v pos into switch, Black should be 12v pos everywhere when switch is on

[M 750K6]

👍  thanks Bryan.

Tomorrow, I will test the switch first. I think it's helpful that I'm getting power to the parking lights on key switch position 2. suggesting my issue is localised to the switched live circuit, and to that part that is common before it separates into the various draws (the various lights, console warning bulbs, kill switch, starter button etc.).

I've been thinking, plugging in my heated kit hasn't blown a fuse. So I'm wondering about what I might have touched, which may have caused this. Whilst I've recently touched almost everything on the bike (engine out and frame completely stripped), when the bike came to me, the main loom was attached onto the wrong frame tube. When I reassembled it, I put it back to the factory routing. This caused a bit of a kink in the front section of the wiring loom, after it came out into the area to the front of the tank and up into the headlamp bowl.

I'm wondering if, assuming the key switch tests ok, I may have a break in the loom around that kink. So I will go on to test continuity on the black wire, from the key switch to its connector inside the headlamp bowl.

I'll be scratching my head again if that checks out OK. I guess I'll need to check the wiring from the bowl into the right-hand switchgear.

[bryanj]

The most common problem is a high resistance connection between red and black INSIDE the switch, the park system uses different contacts in the switch.

What tends to happen is the secret additive (sh1t)  builds up on the contact part making high resistance which makes heat that melts the plastic allowing the contacts to sink in which makes connection even higher resistance, more heat, more melt till no contact =no go

[seanbarney41]

That is EXACTLY what I found inside my switch.

[bryanj]

You aint the first, or probably in the first 10,000 and definately wont be the last

[HondaMan]

I've seen that scenario in several (too many) of the EMGO-made switches from China. The contact's substrate is plastic instead of the original phenolic (which later became Bakelite black plastic) in the OEM switches, and is simple plastic (ABS) in the knockoff switches. To add insult to the injury: the contacts are both undersized and copper instead of properly-sized silver, and the wires (this is the big clue to who built the switch) are 20 AWG size instead of the needed 18+ (almost a 16 AWG) size. This makes the contact heat up, then they sink into the plastic, and then...the engine stops in 70-MPH freeway traffic.

Yeah. That's where mine went out...

[M 750K6]

Thank you guys.

All fixed. No continuity across the key switch in position 1. It turned out to be the terminal on the back of the switch that holds a single red. I cleaned it and re-soldered. Looks like new, so hopefully, I'm good to go. It is all live now.

I might fashion a little jumper kit, that I can carry with me in my toolkit, which I can plug into the loom, if the solder breaks again. 👍

[jukku]

Here you have Wiring Diagram for K6
http://manuals.sohc4.net/cb750k/technical_reference/WD750K6.pdf

[M 750K6]

Excellent.  I'll print that off. Thanks.

[seanbarney41]

yes sir...that jumper kit is a good idea.  Especially if you have a 77/78 model cb.  The switch that is used in the dashboard is even more trouble prone than the earlier one that is mounted under the tank.

[willbird]

Thank you guys.

All fixed. No continuity across the key switch in position 1. It turned out to be the terminal on the back of the switch that holds a single red. I cleaned it and re-soldered. Looks like new, so hopefully, I'm good to go. It is all live now.

I might fashion a little jumper kit, that I can carry with me in my toolkit, which I can plug into the loom, if the solder breaks again. 👍

When I was old enough to start riding a CL175 around the back 40 as fast as it would go we had one for me to ride, I rode it for 2 years 16-18 too once I got my temps and my endorsement. But at home it just had the plug from an old switch with each pair of wires twisted together. My dad had used one of those kits to relocate the OEM switch up on the bars and rain got into that switch and ruined it.

Bill

[M 750K6]

Ref the wiring diagram. Printed offcand with my manuals 👍.  I think my bike is slightly different to the diagram. E.g. on key switch position 2, both my tail and a front pilot light are lit. Maybe a UK thing? But looks similar otherwise. Thanks

[M 750K6]

yes sir...that jumper kit is a good idea.  Especially if you have a 77/78 model cb.  The switch that is used in the dashboard is even more trouble prone than the earlier one that is mounted under the tank.

I'm thinking 2 wires,  with female blades each end and one labelled red and black, to remind me. Scary how easy they are to steal...

[seanbarney41]

yes sir...that jumper kit is a good idea.  Especially if you have a 77/78 model cb.  The switch that is used in the dashboard is even more trouble prone than the earlier one that is mounted under the tank.

I'm thinking 2 wires,  with female blades each end and one labelled red and black, to remind me. Scary how easy they are to steal...

yup, that is exactly what I use, ...but was not gonna mention on open forum lol

[M 750K6]

Needs the tank off though. Which has the 'deterrent' of the seat latch lock. Probably easier to use a screwdriver in the ignition... oops, done it again!

[HondaMan]

You can install a small relay (12 volt, about 1" cube) and switch that with the Black wire from the switch to prevent it melting that wire off again. I did that some years ago after mine melted off one day on my then-new Chinese-made EMGO switch - in traffic.

[M 750K6]

I'm interested in this, but a complete electrical novice. Is there a guide anywhere on the relay I'd need and where / how to wire it in?
Thanks. 👍