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Discussion Starter · #1 ·
Recently the battery light on my 1993 900 Superlight has been coming on intermittently while riding. It will stay on for maybe 15 minutes; then go off & not come on again for an hour. Admittedly, diagnosing electrical issues is not my strong suit. But I plan to do some basic battery checks, as well as look for any loose and/or corroded connections. However, in the meantime, I would appreciate any ideas of what the problem might be. This will certainly help me to focus my search.

Thank you kindly.
 

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I'd start at the battery terminals then the chassis ground...look for corrosion... disconnect and clean em with a wire brush and sandpaper...if that doesn't fix it and your battery is not too old the next step would be to read voltages coming out of the alternator
 

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Discussion Starter · #3 ·
I'd start at the battery terminals then the chassis ground...look for corrosion... disconnect and clean em with a wire brush and sandpaper...if that doesn't fix it and your battery is not too old the next step would be to read voltages coming out of the alternator
The battery is a few months old. The terminals are clean since I recently made to remove the battery to rebuild the carbs. But I will check the chassis ground, as well as the alternator voltage.

Thank you for the suggestions.
 

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My SS rubbed through the VR wires and was shorting against the frame. Unplug and clean and lube all your electrical connectors, and fuses . 96 has a second ground low on right side of bike by brake master, yours might too. The connector that taps from your hot between the battery and solenoid can be an issue. I eliminated it and ran a pigtail from the battery to supply the rest of the bike and remove resistance from the starter circuit. Aftermarket starter wiring upgrade is , well, an upgrade.
 

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Discussion Starter · #5 ·
My SS rubbed through the VR wires and was shorting against the frame. Unplug and clean and lube all your electrical connectors, and fuses . 96 has a second ground low on right side of bike by brake master, yours might too. The connector that taps from your hot between the battery and solenoid can be an issue. I eliminated it and ran a pigtail from the battery to supply the rest of the bike and remove resistance from the starter circuit. Aftermarket starter wiring upgrade is , well, an upgrade.
Thank you. I plan to follow through on your recommendations after to verify that the issue is not the result of a problem in the charging system.
 

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Discussion Starter · #6 ·
Well, after cleaning the battery terminals & all connectors to the terminals, I proceeded to check/clean the battery ground. Next I traced the various wires from the alternator & the regulator/rectifier & cleaned all of the connectors. At this point there was no obvious problems.

So I verified the battery voltage after a few hours off of the charger. Good. Next I noted the voltage at the battery at idle, as well as at 3,000 rpms (& above). Voltage increased from about 13.5V to 15.5V. This suggests that the alternator is doing it's job. (However, I might mention that during this test the battery idiot light was not on).

Finally, I decided to see if any of my work resolved the issue of the battery idiot light intermittently turning on while riding. After 3 miles into the ride, the light came on & remained on for 15 miles. Then it switched off for the next 35 miles. When I got home (the light was still off), I checked the voltage at the battery which was 13.25V.

So, I am perplexed. Is there an intermittent problem somewhere in the alternator or the regulator/rectifier? A bad connection or short to ground? A faulty battery idiot light? Any ideas would be appreciated. Oh, the only thing I forgot to check was duc96cr's suggestion to check the wire from the positive terminal of the battery & the solenoid. I'll do that tomorrow. Thank you!!!!
 

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If this was a car I would look for a faulty voltage regulator...it's got to have one somewhere...I'd also try to get a read of the voltage when the light comes on...if it comes on and the voltage output is still high than it's a read error...but if the voltage dropped it's a regulator issue...I have know knowledge on your model...only speaking in general terms...this would be my next point of inquiry
 

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Discussion Starter · #8 ·
If this was a car I would look for a faulty voltage regulator...it's got to have one somewhere...I'd also try to get a read of the voltage when the light comes on...if it comes on and the voltage output is still high than it's a read error...but if the voltage dropped it's a regulator issue...I have know knowledge on your model...only speaking in general terms...this would be my next point of inquiry
Good point. The voltage regulator is an aftermarket unit I installed years ago. I might have the OEM unit which I could swap out. Thank you.
 

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By all means, swap it out !
 

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The voltage regulator and the alternator rectifier are built into one unit on most bikes.
When does the light come on? Low rpm with indicators and brake lights on?
 

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Discussion Starter · #11 ·
The voltage regulator and the alternator rectifier are built into one unit on most bikes.
When does the light come on? Low rpm with indicators and brake lights on?
The light does not come on when I start the bike & it's at idle. It comes on when the bike is running in the 3,000 - 4,000 rpm range. However, while riding if I decrease the rpms (or even shut off the bike & restart it), the light remains on.
 

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Discussion Starter · #12 ·
Well, it appears that I have stumbled on the cause of the intermittent battery light issue. By rechecking the voltage output at the battery, the output was as follows: 12.5V @ 1,100 rpms, 15.8V @ 3,000 rpms & 16.0V @ 4,000 rpms. These seems to be way excessive. And, finally, when I removed the headlight for easier access to the regulator/rectifier wiring, I discovered that the plastic electrical connector to the headlight was partially melted. So, unless I have missed another contributing factor, the problem appears to be a faulty regulator/rectifier. Does this sound correct?
 

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Well, it appears that I have stumbled on the cause of the intermittent battery light issue. By rechecking the voltage output at the battery, the output was as follows: 12.5V @ 1,100 rpms, 15.8V @ 3,000 rpms & 16.0V @ 4,000 rpms. These seems to be way excessive. And, finally, when I removed the headlight for easier access to the regulator/rectifier wiring, I discovered that the plastic electrical connector to the headlight was partially melted. So, unless I have missed another contributing factor, the problem appears to be a faulty regulator/rectifier. Does this sound correct?
Yes....your rectifier is spastic...as it heats up resistance changes and it can't do the math...dump it....ride on

I urge a second opinion...14.4 should be operating voltage.....no more....if your getting a reading of 16 I might be missing something in the equation....that is high...high enough to foul the battery....if you recently replaced it, I'd budget another....that high a voltage can wreak havoc
 

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Discussion Starter · #15 ·
Well, it appears that I have stumbled on the cause of the intermittent battery light issue. By rechecking the voltage output at the battery, the output was as follows: 12.5V @ 1,100 rpms, 15.8V @ 3,000 rpms & 16.0V @ 4,000 rpms. These seems to be way excessive. And, finally, when I removed the headlight for easier access to the regulator/rectifier wiring, I discovered that the plastic electrical connector to the headlight was partially melted. So, unless I have missed another contributing factor, the problem appears to be a faulty regulator/rectifier. Does this sound correct?

And thinking ahead, there seem to be 2 options for a new aftermarket regulator/rectifier: the Electrex RR51 (which is currently installed) & the ElectroSport ESR510s or the ERS515. I would appreciate any recommendations. Thank you kindly.
 

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Well, it appears that I have stumbled on the cause of the intermittent battery light issue. By rechecking the voltage output at the battery, the output was as follows: 12.5V @ 1,100 rpms, 15.8V @ 3,000 rpms & 16.0V @ 4,000 rpms. These seems to be way excessive. And, finally, when I removed the headlight for easier access to the regulator/rectifier wiring, I discovered that the plastic electrical connector to the headlight was partially melted. So, unless I have missed another contributing factor, the problem appears to be a faulty regulator/rectifier. Does this sound correct?



And thinking ahead, there seem to be 2 options for a new aftermarket regulator/rectifier: the Electrex RR51 (which is currently installed) & the ElectroSport ESR510s or the ERS515. I would appreciate any recommendations. Thank you kindly.
I might give Rick's a look over the electro sport

The esr515 is supposed to run cooler...Rick's has the hot shot version which uses mosfets to the same effect...I'd probably go Rick's after reading reviews on the esr's...either way it looks like Rick's has good information to read on in any event

https://ricksmotorsportelectrics.com/l/rectifier-regulators
 

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Discussion Starter · #17 ·
I might give Rick's a look over the electro sport

The esr515 is supposed to run cooler...Rick's has the hot shot version which uses mosfets to the same effect...I'd probably go Rick's after reading reviews on the esr's...either way it looks like Rick's has good information to read on in any event

https://ricksmotorsportelectrics.com/l/rectifier-regulators
Thank you. I will definitely follow up with Rick's. Much appreciated.
 

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Yep it's not uncommon for motorcycle regulators to go bad. Max voltage is 15v DC, anything higher will cook the battery and it won't last long.
 

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Discussion Starter · #19 ·
At the moment, I am looking at the ElectroSport ERS515, the Electrex RR51 & the Rick's Motosport Electrics MOSFET technology unit.

BTW, can someone suggest a source for the plastic electrical connector for the headlight on a 1993 Ducati 900 Superlight? Apparently Ducati only sells the complete wiring harness. Thanks!
 
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