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Question
1993 Yamaha virago 750,I was riding at night,then like a light switch the lights went dim and I drove it for about 3 minutes,parked it for the night,the next morning the battery was dead.How can I start the process of finding out what is wrong?Thank you for your time.

Answer
Hi Tom,

I am not sure if your battery is okay but you will have to have it charged or replaced
to test the bike's charging system.

You have to determine if the stator or the regulator/rectifier is at fault
or something else entirely.

The stator should have a connector coming out of the engine which has
three white wires in it.

Disconnect the plug and with a multimeter check that none of the three white
wires are grounded. They should not have any connection to ground or the bike
frame.

If they pass that test then you can start the bike with the plug disconnected.
Set your multimeter on "AC" voltage.
Check the voltage between any two of the three white wires.
Speed the engine up a bit and watch your voltage readings.
Between any two of the wires should put out about 30-60 "AC" volts.

If this seems okay then it is logical to check your regulator connector, ground
and wiring. Finally reconnect the connector and put your multimeter on the battery
terminals. See what the "DC" voltage is at a fast idle.

If it is reading the same as the battery or above 15 volts then shut it down
and replace the regulator.

If the stator reads low or no voltage on any two of the three wires
then the stator may be gone.

Do these tests with a known good battery to prevent any problems
arising from a shorted battery.

If you get the stator, regulator and battery fixed it should work.
If you see any place the wiring has been hot that might be a problem too.
Check and clean any connectors relevant to the charging system.

Let me know if you need more info.

WS
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Motorcycle Repair

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Wayne S.

Expertise

Licensed Motorcycle Mechanic, Knowledge of motorcycles from 1960 up, Japanese, British and most other brand motorcycle repairs.

Experience

Worked for Yamaha, Honda, Suzuki, Kawasaki British: Triumph, Norton, BSA Other: Most Scooters and Mo-Peds

Publications
Canadian Motorcycling magazine article

Education/Credentials
Licensed Motorcycle Mechanic

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