Question about 2004 Yamaha DT 125 R

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I have a dt125 4j3 model no headlamp electrics i have put a volt meter on and it reads a minus voltage when lights turned on side light is ok it has had a new voltage regulator and rectifier and magneto windings any idears please thank you .

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Ive had a similar problem with my 2007 dtx, but with the rear light and power valve. it turned out to be a dodgey connector. i dont know if the colours would be the same but it was the brown cable (the live +12v) coming from the ignition, it connected to 7 other wires and 3 were rusted off. it seems to me that yamaha have some kind of problem with their electrical skills, good luck!

Posted on Jul 21, 2010


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My 2003 883 Sportster, when turning on ignition key, instrument panel andheadlights turn on.When ignition button is pushed get a loud click, then nothing.No ignition, and lights go out.

Hi Anonymous, perform the following tests:
1. Fill acid type batteries to proper levels.
2. Charge battery overnight at 1-2 amps you need 12.5 volts or better after charging.
3. Hook up battery positive cable, then with your multimeter on the milliamp scale connect one lead to the negative battery post and the other lead to the ground cable. Meter should read 3 milliamps or less, 10 milliamps with a radio, 15 milliamps with radio and CB. If your meter reads higher you need to isolate the circuit by pulling fuses and circuit breakers one at a time and observe meter for drop in aprerage then get out your test light and track down the short in that circuit.
3. Make sure all connections are clean and tight especially the negative cable at both ends.
4. Hook up volt meter to battery and start engine, if meter falls below 9.5 v while cranking replace battery.
5. With engine running at 3600 RPM battery should read 14.3-14.7 volts if not continue tests.
6. Unplug voltage regulator from alternator at crankcase by front of primary cover.
7. To test voltage regulator go to:
8. With ohm meter, one lead grounded, touch alternator pin meter should read infinity, if not replace stator.
9. With ohm meter, both leads touching alternator pins meter should read 0.1 to 0.2 ohms on 1989 and later models. 0.2 to 0.4 ohms 1988 and earlier models, if not replace stator.
10. With volt meter set on AC scale, both leads touching alternator pins meter should read
16 to 20 volts AC for every 1000 RPM'S 1989 and later and 19 to 26 volts AC for every 1000 RPMS. If not replace rotor.
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My explorer, Eddie Bauer edition had an electrical problem, when you switched to the high beam lights, you could a hear a crackling and the light would go off, but if you switched back to the low beams,...

Or the headlamp switch or the low high dimmer switch ! Does it DRL - day time running lamps ? Ignition switch has nothing to do with the headlamps or power locks . Also if the ignition switch was the problem the vehicle wouldn't start . Here is a web site for wiring diagrams Enter your vehicle info. year , make , model an engine size ! Under system click on lighting then under subsystem click on headlamps ! Then click the search button , three links will pop up . Click them one at a time ! With a DVOM - digital volt ohm meter test for B+ voltage at the headlamp switch , turn on the headlamps on low an check for B+ voltage coming out . Check on high beam as well . Here are a couple of videos , check em out .
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Recently having problems with my 2000 Fatty not holding charge. What should stator be putting out on voltage meter? Voltage meter climbs as rpms go up, I would presume that this indicates stator ok? Bike...

First, take your battery somewhere and have it load tested. Fat Boys are tough on batteries as the battery sits in the "horseshoe" oil tank and is subjected to high temperatures due to the hot oil in the tank. Battery life is typically two years although I've seen some go longer and some not last that long. Have the battery tested before you start spending money.

To check the stator, you unplug the regulator at the engine case. Down inside the plug you'll see some electrical connectors. Connect a DVOM (digital volt ohm meter) to these connectors (one lead to eac pin) and put the meter in the 50 volt or higher range AC voltage. This is important that your meter be set to measure AC voltage because at this point, the voltage is indeed an Alternating Current voltage coming out of your alternator. Start the engine and bring it to a high idle. You should be reading over 20 volts AC. The book says that you should read 12-18 volts per 1000 engine RPM. If your engine is turning 2000 rpm, your meter should read 24-36 volts AC.

To test the regulator, first charge your battery to a full charge. Then connect your DVOM across the battery, red to positive, black to negative. Put the meter in the 20 volt DC range. Start the bike and bring it to a high idle. The voltage will start at somewhere around 12.5 volts and climb to about 14.5-15 volts. This would indicate that the regulator MAY be alright.

Now, have you changed any of the lights on your Fat Boy? I've seen people change and add lights to the point where their alternator could no longer put out the current necessary to handle the load. If this is the case, you may need a higher out charging system.

I don't know where you're located but $260 seems quite high for a voltage regulator.

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