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TOPIC: RT2 12 volts at headlight.....blown bulb !!!

RT2 12 volts at headlight.....blown bulb !!! 09 Feb 2019 08:19 #1

  • Mauser
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Any idea's why I'm getting 12 volts at the headlight ?, both main and dipped would have thought if the regulator had gone it would been much higher ?....
Ahh looking at the book she doesn't have a regulator just a rectifier ? says between 5.5volts and 7.5volts depending on RPM....
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RT2 ~ XR650R ~ DT175MX ~ ZX12R ~ XJR1300 ~ DT125LC ~ XR250R ~ XL125R ~ RD350LC ~ MT50 ~ GPZ1100

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RT2 12 volts at headlight.....blown bulb !!! 09 Feb 2019 09:09 #2

  • MarkT
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Correct, no regulator on early models, just rectifier. The simple magneto electrical system has fixed strength magnets spinning around the stator coils which means the electrical output is fixed at a given rpm.

In contrast, alternators and DC generators that vary the electrical output do so by using electromagnets so the magnetic field can be varied to raise or lower the electrical output depending on load which keeps the voltage in check.

On these simple fixed magnet systems, magneto output is matched to the electrical load which is what controls the voltage. Remove a load (bulb burns out or even missing or bad battery) and voltage goes up too high. Add some extra bulbs or a higher wattage headlight and the voltage drops too low. Here is an excerpt from an early Yamaha manual:




Adding a regulator to the headlight circuit is an excellent and highly recommended modification... the electronics required just weren't available or were too expensive back when your bike was new... in about 1976 Yamaha started using a regulator from the factory that basically adds load when it senses the voltage is too high... there is a service bulletin in the Tech Library on this modification using the one-wire Yamaha regulator. DEET has also posted some great information including a "regulator shootout". He recommends the factory one-wire regulator or a three-wire regulator as others don't work. Searching the forum will come up with tons of information on the "voltage regulator" topic.
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1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

RT2 12 volts at headlight.....blown bulb !!! 09 Feb 2019 09:26 #3

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That's amazing thanks Mark, I have been running her without a battery :), waiting for a flasher unit to arrive....sounds like I have killed the bulb with over voltage. I have a 6volt regulator somewhere from a DT175MX 1 wire version I will have a play and report back I would guess I just take the supply from the lighting coil through the regulator ?.

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RT2 ~ XR650R ~ DT175MX ~ ZX12R ~ XJR1300 ~ DT125LC ~ XR250R ~ XL125R ~ RD350LC ~ MT50 ~ GPZ1100

RT2 12 volts at headlight.....blown bulb !!! 09 Feb 2019 10:09 #4

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The factory 175MX (DT175 here in the US) headlight circuit regulator will work perfectly!

I recommend teeing it into the dark blue gauge illumination wire circuit on the early bikes as recommended in the service bulletin. This wire is in the headlight circuit and is "hot" on both low and high beam.

The problem with inserting the regulator into the headlight circuit wire right off the stator on the early models is that the headlight can be turned off... and with the headlight off the regulator will have to take ALL the headlight power and try to keep the voltage down which can burn the regulator up if you ever ride around with the headlight off. The dark blue gauge illumination wire only has power when lights are on so it's safe to have the regulator connected there. On later "always on" headlight bikes it doesn't matter.

Link to bulletin:

yamaha-enduros.com/index.php/workshop/se...ulators/viewdocument




.

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1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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RT2 12 volts at headlight.....blown bulb !!! 09 Feb 2019 10:35 #5

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MarkT wrote: The factory 175MX (DT175 here in the US) headlight circuit regulator will work perfectly!

I recommend teeing it into the dark blue gauge illumination wire circuit on the early bikes as recommended in the service bulletin. This wire is in the headlight circuit and is "hot" on both low and high beam.

The problem with inserting the regulator into the headlight circuit wire right off the stator on the early models is that the headlight can be turned off... and with the headlight off the regulator will have to take ALL the headlight power and try to keep the voltage down which can burn the regulator up if you ever ride around with the headlight off. The dark blue gauge illumination wire only has power when lights are on so it's safe to have the regulator connected there. On later "always on" headlight bikes it doesn't matter.

Link to bulletin:

yamaha-enduros.com/index.php/workshop/se...ulators/viewdocument




.


I'm too impatient lol....luckily I only got as far as making a connect in point to the yellow wire from the stator....then your reply popped up....phew. Just reading the pdf now....thanks again Mark
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RT2 ~ XR650R ~ DT175MX ~ ZX12R ~ XJR1300 ~ DT125LC ~ XR250R ~ XL125R ~ RD350LC ~ MT50 ~ GPZ1100

RT2 12 volts at headlight.....blown bulb !!! 09 Feb 2019 10:44 #6

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I cannot find the "Dark Blue" wire Mark....even my son15 with his young eyes can only find the normal blue....any idea's ?
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RT2 ~ XR650R ~ DT175MX ~ ZX12R ~ XJR1300 ~ DT125LC ~ XR250R ~ XL125R ~ RD350LC ~ MT50 ~ GPZ1100

RT2 12 volts at headlight.....blown bulb !!! 09 Feb 2019 11:03 #7

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I'm pretty sure that there's only one shade of blue in the harness and if Yamaha chose to call it "Dark", then dark it is!

That's the one I'll be using when I wire in my own regulator.

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RT2 12 volts at headlight.....blown bulb !!! 09 Feb 2019 11:20 #8

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Bikes with neutral lights in the speedo/tach had a "light blue" wire. In the early years, that was only the 125 and 175 models.

Here's a picture from a later bike showing the gauge harness with the "light blue" aka "sky blue" wire to the right of a couple of "dark blue" wires.

In other words, those "regular blue" wires are the right color. :Buds


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1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

RT2 12 volts at headlight.....blown bulb !!! 09 Feb 2019 11:43 #9

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Thanks Mark - that makes sense now!

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RT2 12 volts at headlight.....blown bulb !!! 09 Feb 2019 11:49 #10

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My original reply just said "blue"... I edited to "dark blue" when I posted the link to the bulletin because that's what Yamaha's doc said and I remembered the little bikes having a light blue wire... someone with a 125 or 175 might read "blue" and connect to the wrong wire. Sorry for the confusion.

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1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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