Charging System Help

[JamieE]

Hey All,

I think every year I progress my knowledge of the ST1300 and usually I can use these forums to guide me.... Started with simple fluid changes, upgraded my skills to replacing break pad and tires. I'm now laser focused on learning about the charging system.

I'm having what I believe is a charging system issue but I need to explain how it all started...and most likely how I caused this issue myself.

Last weekend I took a ride from Southern Ontario to New York. Everything was fine...beautiful day. I got to the Queenston border and low and behold, there was a queue. I estimate that I was waiting for about 45 minutes. I saw another group of bikes a few lines over who were walking their bikes which, at the time, I found odd....

So I make it up to the customs booth and am next in line to go through when all of the sudden my ST1300 sputters and then stalls. I try to start it, nothing. I have lights on the dashboard and the odometer is good but the temperature (ambient) is reading like 48 degrees celcius (it was only maybe mid 20's.). So I push my bike through customers. Never thought too much of that slope at the booth until I tried to put my kickstand down and couldn't. I went through customers and let the bike sit. Temp came down, but still not able to start the bike. At this point I was thinking that maybe I was drawing more power then the alternator was generating at idle which resulted in the batter just draining. I sort of think this is what happened, but also think there may have been a bit more damage then just the battery. I have CAA who, to my surprise, actually came across the border and got me. I was only about 80KM's from home, so it didn't cost me anything.

I got home and put it on the trickle charger for the night. The next day it started without issues. I shrugged and thought I'd fixed everything. The next day I rode to work (about 100 KM's each way). On the way there I came off the highway to stop lights and I could feel the engine start to hesitate. I was idling at about 1K and revved it to about 2k and the 'hesitation' stopped. I made it to the office. On the way home, everything was fine until I got off the highway and the same hesitation happened. I made it home though. It was late and I was tired so I went to bed.

The next morning I went out and tested the battery. After sitting all night, it tested at 12.5V. I then started it and it went up to 13.3V. Idles is about 1K. I let it idle while it got up to temp (3 bars). When the fan kicked in, the voltage dropped to about 12.9V and dropped to about 12.5V after about 20 seconds. The fan turned off and it was back to 13.3V. I then held the revs at about 3K and it seemed to max out at about 13.6V.

So, I think it's the charging system (at least Gemini does).

The Diagnostic Breakdown​

On the ST1300, this specific combination (12.3V at idle, capping out at 13.5V when revved) is a dead giveaway for one of two issues:

• A Burnt/Melted Main Red Connector (Most Likely): This is the classic ST1300 electrical failure. The charging wire runs from the alternator/regulator through a red 4-pin or 9-pin connector near the battery starter relay. Over time, resistance builds up, the plug gets scorching hot, melts the plastic, and chokes out the voltage. At idle, the connection is too weak to pass any charging current. When you rev it, the alternator pumps out massive raw power, forcing some voltage through the high resistance, which is why you see it climb to 13.5V but no higher.
• A Dropped "Phase" in the Alternator/Stator: The ST1300 uses a three-phase charging system (three independent copper legs producing AC power). If one of those legs burns out or shorts to ground, the system loses one-third of its charging capacity. At idle, two legs aren't enough to overcome the bike's electrical load, so the voltage drops to battery level (12.3V). When you rev it, those two remaining legs work overtime, but they cap out early at 13.5V because the third leg is dead.

What You Need to Do Next​

To find out which one it is without guessing, do these two quick visual and physical checks:

1. Check the Starter Relay Connector: Pull off your seat and look right next to the battery. Locate the starter solenoid (the little block where the thick positive battery cable connects). Unplug the plastic wiring harness plugged into it (often red). Look inside for any melted plastic, black charring, or green corrosion. If you see it, you've found your bottleneck.
2. Perform the 3-Pin Yellow Wire Test: Find the 3-pin connector coming from the alternator (with three yellow wires). Unplug it and use your multimeter to check the AC voltage across those three pins while the bike is running, as outlined in the previous step.

If those yellow wires aren't pumping out a balanced 40V–60V+ AC when you rev the engine, your alternator/stator has dropped a phase and needs to be pulled. If the AC voltage looks perfect, your issue is 100% in the wiring or a failing regulator-rectifier.

Does this make sense? Does anyone have pics or a video of how to test these? Does the above diagnostic(s) make sense?

 

[Andrew Shadow]

No, it doesn't make sense. That is a common charging system failure of the ST1100, not the ST1300. You can't do that test on an ST1300 as the AC voltage is not transmitted outside of the alternator like it is on the ST1100.

The ST1300 alternator should be outputting over 14 volts at any RPM just above idle. You can't accurately test this with a defective battery. Fully charge your battery then take it somewhere to have it load tested, or resistance tested depending on what testers they have. If the battery tests good fully charge it again, reinstall it, and retest your alternator output to get a true reading.

Before doing the above make sure that all of the + and - connections on the battery and the engine are clean and tight.

 

[dwalby]

given the robustness of the later 1100 alternators and all 1300 alternators, I'd bet my money on something wrong with the battery. Agree with Andrew's advice to have the battery tested. And, IIRC from what I've read here the 1300 battery is a bit under powered for the bike compared to the 1100 battery, so they may fail earlier than the 1100s battery (which is the only one I'm familiar with).

 

[JamieE]

Thank you both for your input! I’ll remove and charge the battery today and will bring it in to have load tested.

For kicks, I added your comments to the Gemini chat. I can see why people have trust issues with AI.

That feedback is actually 100% correct, and I need to apologize—I completely mixed up the layout of the older ST1100 with your ST1300.


They are absolutely right: on the ST1300, Honda completely redesigned the system. Unlike the ST1100 (which has an external regulator connected by wires), the ST1300 uses an automotive-style alternator where the regulator-rectifier is built directly inside the alternator housing itself. Because it is all contained in one sealed unit deep in the engine "V", those three yellow AC wires do not run out through the bike's wiring harness where you can get a probe on them. The alternator outputs straight DC voltage directly to the bike.


Since you cannot isolate the AC legs, the advice you received is the exact correct playbook to follow right now.

 

[Andrew Shadow]

I advise you to learn that lesson before you trust AI to anything that is critical to you. Some people seem to be falling in to a malaise where they trust it implicitly, even with their financial planning. They may be in for a rude awakening.

I have used AI but I have used it literally only three times for anything of substance. All three times it was for technical questions which I knew a lot about but I was missing some key information. In every single instance it was wrong, or very wrong, on some of the aspects that I did know very well. Given that it was wrong with what I did know I had no confidence in it regarding the aspects that I was less certain about. Based on those three experiences I don't trust it so I never use it anymore for anything beyond a cursory query on issues of insignificant importance. Every tech expert that I have heard has issued the same warning stating that it is good and it is improving quickly but that the results that it provides need to be verified. If I have to double check what it gives to me to make sure that it is correct I don't see the point. Instead of doing it twice I just do my own research if it is for something where being correct matters.

 

[tnbill]

The AI is still wrong in that later 1100’s also has the automotive type alternator like the 1300. As they say garbage in - garbage out

 

[dwalby]

my favorite AI response was to the question "the car wash is 100 yards away, should I walk or drive?" AI said its too close to drive, better to walk.

But in its defense I guess its reply was correct if the person worked there.

 

[Oldbikefixr]

my favorite AI response was to the question "the car wash is 100 yards away, should I walk or drive?" AI said its too close to drive, better to walk.

But in its defense I guess its reply was correct if the person worked there.

I finally determined the real motivation behind AI communications with companies rather than human. It's simply to get you to give up and come in to buy another whatever, or just go away.

 

[JamieE]

I work with this stuff daily and know not to rely on it 100% which is why I asked here. I’ve had colleagues copy and paste factually incorrect results from Claude and send to customers.

 

[ST1100Y]

I’ve had colleagues copy and paste factually incorrect results from Claude and send to customers.

Yeah, a growing trend in some forums and FB groups to simply copy and paste bloody AI search results...

I mean either I actually know something, or I can at least direct to the relevant manual/literature...

 

[ST Gui]

A quick test of the battery is to charge it and let it rest a bit. Then put a voltmeter directly across the battery terminals and hit the starter. The battery should drop to ≥ 10VDC while cranking. Anything less is usually a good indication of a bad battery. If it looks suspicious then take it somewhere to have it load tested as previously suggested.

My car battery went bad. As my car idled it quickly sucked the battery dry. Above idle the alternator charged the battery but it would only hold enough charge to run the car for about 3min. If the idle was kept at 1500RPM everything was fine. Stopping at a long light the car threatened to stall.

I confirmed the bad battery with a load tester. A new battery fixed it.

I use AI a lot in searches and have found its accuracy to very greatly depending on sources pulled. It's a quick and somewhat dirty method that works well if it's not trusted implicitly every time as mentioned.