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Discussion Starter · #1 · (Edited)
Hi all, hope everyone is well

Was hoping to get some help from the wider community on a charging issue I’ve been having for a while...

I have an 05 Kawasaki z750 which was running fine last year around May when I got it. However the bike unexpectedly died on me in December time. I thought nothing of it as I didn’t know about charging systems at the time and just assumed the battery was dead so charged it and carried on riding. Then it happened again while riding, so I replaced the battery with a new one thinking it would solve the issue. Unfortunately the bike died again this time on the m6 😭
I then started looking into charging issues

I did the charging voltage test- DC across battery terminals at 4K rpm and was getting around 12 volts when it should have been around 14...
So replaced regulator rectifier - that seemed to work as charging voltage was now around 13.89 and increased to about 14 when revving the bike.

However the bike died AGAIN on the road after replacing it!
When I wheeled it back home to check the charging voltage it was no longer charging was stuck at 12 volts again

I checked the stator, did the unloaded test at 4000 rpm ACV got around 55v across all phases checked coil resistance everything was fine

I replaced it anyhow as apparently they could fail under a load, however it didn’t fix the issue

so I got a new reg rec, still didn’t fix it

I then went to check if the AC voltage was getting to the reg rec connectors which it was.

strangely, with the RR connected, I couldn’t get a reading of any AC voltage at the RR end...is this normal?

I’m at a loss here I have no idea what else to do...
I tested the voltage coming out of the white wire from the RR as this is the one that goes to the battery...
I assumed it should show 14.4 volts roughly indicating the RR is working but the voltage is getting lost through the positive lead from the RR to the battery but I was only getting 11 or so volts ...the same as the voltage at the battery
Does this mean the RR is not putting out 14 volts at all? I connected the white wire to the battery negative for this test

The white wire from the RR goes to the battery through the main fuse connector so I checked it and found it had corrosion...I tried getting it all out but it had no effect on the charging. Also the fact that the replacement RR was charging the battery indicates to me that there was no wiring fault. But what caused the bike to stop charging then??

I hope this is making sense to someone!
I should also mention that the headlight does not turn on and the indicators flash intermittently.

the new RR is still getting hot when the bike is running so there is current getting to it??
Any thoughts or ideas would be greatly appreciated and I am happy to answer any questions for further diagnosis!

so just to clarify

  • New stator
  • New regulator rectifier that I know works as it’s an oem used part which the seller said produced 14.1 V at 3k rpm
I also checked the voltage across the starter motor cable while idling as they tend to draw current and charging voltage if the starter relay is bad. It wasn’t showing any voltage so I think that‘s fine

I also followed the attached flow chart and everything checks out

I look forward to any responses!


2 Posts
Discussion Starter · #3 · (Edited)
Solved the problem - hopefully this might help others out there who may bump into the same issues

Had a look at the wiring diagram and found that the negative BK/Y (black and yellow) wire for the regulator/rectifier (RR) grounded to a joint connector (joint connector B.) Found this on the bike in the main loom under the right hand side fairing. As you can see in the images attached one of the pins was severely burnt / blackened. Instead of replacing it I bypassed the loom;

I T-spliced a 12 gauge wire into the RR's BK/Y negative wire a few inches from the RR and connected this up to the battery negative terminal and? problem solved. Headlights came back on after this too. This makes it so that the excess voltage produced from the stator (a LOT) grounds straight to the battery negative terminal with a much shorter and thicker wire, the way it should be produced straight from the factory really.

For any charging issues I may have with future bikes I'm going to start by connecting the RR straight to the battery. Ground wire first. then positive wire with a 30A fuse if it doesn't work.

Especially before replacing things like the stator and RR which is expensive and unnecessary hassle. Turns out the original RR was fine after all as it is currently charging at 14.8 at idle. Result.

But hey, everything's a learning curve


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