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Discussion Starter #1
Just went for first ride after winter. Had full charge on battery, fresh gas. Got within 1/2 mile of home and bike started running poorly pulled into drive she died. Looked her over some and tried to start and battery is dead just clicks. I'm going to charge the battery overnight and see what happens. What my question is if it starts up and runs fine can it be as simple as a new battery? But why would that affect how the bike was running? Thanks in advance
 

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Sounds like your alternator isn't charging, and the battery was draining during your ride. If that's the case, count yourself really lucky that it didn't pack in miles from home! :)
The misfire will happen when battery voltage declines to the point where it is struggling to generate sparks at the plugs.
 

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I agree with Kevin. Please do us all a favor and fill out a signature line, with the year and model of your ST, so we don't have to guess.
 

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That sounds exactly like what happened to my SS. It turned out to be the voltage regulator. Charge it up and if it runs good then that would be the next thing I check.

Marc
 

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Charge battery so it'll start. Then with DVM check the charge status with it running. That'll narrow the area you need to investigate. If the DVM shows minimal charge status then either VR (probable) or alternator.
 

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Discussion Starter #6
Thanks for the quick response. Charged up overnight and bike fired right up and ran great. Picked up a Meter to check charge status. What should the meter be reading with the bike running and is there anyway to differentiate between the VR or the alternator.
 

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If the bikes charging system is not working properly the battery will be discharged while riding. Using the volt meter check that the charging system output voltage is 13.6V-14.4V at ~2000rpm.

Hook up the DVM to battery with it set to DC volt. Then read results.

BikeBoy.org - Charging system diagnosis procedure
 

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Discussion Starter #8
Update on my 99 ST4. Went ahead and replaced battery. Hooked up and started bike volt meter reading about 12.5 at 2000 rpm, not good. Started looking at wring and found this (see photo). Was able to separate burnt wires and my meter read 13.8. Here's my question, are all 3 yellow wires the same. Thought I would cut out this one foot section and splice in new wiring. For whatever reason the wiring on either side of connector looks good.
 

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Thought I would cut out this one foot section and splice in new wiring. For whatever reason the wiring on either side of connector looks good.
I advise you to replace more than just one foot of wire.

The stator windings and leads are just lengths of insulated wire. If the insulation fails, the wires short together and the alternating current output of the stator is diminished - often to zero. The voltage differential between stator wires increases as engine rpm increases, so shorting due to damaged insulation is more likely as voltage increases.

The stator wires carry a substantial current, so any point of electrical resistance is a point of heat generation. The connector between the regulator/rectifier (RR) and the stator is THE point of increasing resistance over time due to corrosion — and because it has a higher resistance than the attached wires. Consequently, the connector gets hot — really hot — and because copper wire is a good conductor of heat, the adjacent wires get hot for a substantial distance from the connector. Immediately adjacent to the connector the insulation becomes discolored from internal heat, but more importantly, it looses the ability to insulate its wire from adjacent wires and components.

On Ducatis, the stator wires are run inside a sheath that provides additional insulation from adjacent grounded components, but this causes a problem — inside the insulating sheath, the stator wires are held close together so they touch.

So what happens is — the connector heats the stator wires, the hot wires damage their insulation, the wires short together where they touch inside the sheath (at higher voltages produced at higher engine rpm).

A diagnosis of damaged and shorting lead wires will display normal battery charging voltages on an on-board voltmeter, but at higher rpm the voltmeter will drop to sub-12 volt values indicating that you’re not charging.

When the stator output is shorted out it can damage the internal electrical components of the RR. Often, a new RR will fail soon after replacement because the damaged wiring was replaced only where it showed discoloring adjacent to the connector.

On my 916, I had four RR failures before replacing the stator lead wires. The insulation on the stator wires where it entered the engines side cover was so soft from heat that I could peal it back with my fingernail. Removing the inline connector and soldering the wires directly solved the problem with over heating.
 

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Similar happened to me on a '96 Duc.

VR wires at the connection developed a loose connection or corrosion or both. Lots of resistance and the wires over heated and touched each other on occasion.

I took some spare wire as you intended, used some weather pack connectors from ebay and back in the saddle. Don't sell the ruggedness of the system short. It can take some abuse. You'll know when the wires are fixed and can see the charging voltage. If the voltage doesn't return, next step is to ck the VR. S
 

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The fact that you saw almost 14V with the wires separated sounds very encouraging.
But as Shazaam says, it's worth checking all the way back to where the wires enter the LH housing. Just make sure they're healthy, or do they need to be replaced all the way back to there?

I noticed that the same connector on my ST4s showed signs of yellowing. And a bit of heat noted there while running/charging. After one attempt to tighten those female spade connectors, I decided to cut out the connector and splice the wires together. No more heat...

Oh, the 3 wires are 3 phase, AC, so they don't have a specific order on our bikes.
see: Electrical Service Types and Voltages | Continental Control Systems
3rd illustration down. Of course, our voltages are lower!
 

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Discussion Starter #13
Thanks for all the help, Bike sorted out. Checked out all the wiring and it looked good. Tested the RR and the stator both good. Just went ahead and bypassed the connections and ran new wire. Fired her up and reading 14.5 at 2000 rpm. Just in time for a nice weekend.
 
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