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TOPIC: Headlight keeps blowing out.

Headlight keeps blowing out. 05 Feb 2018 13:48 #1

  • monel12
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Finishing up a 1975 DT 400. All the lights work, but when I rode it last week, it blew out...I know there is no regulator on this bike, and is controlled by the battery, but this is the second headlight I have blown.
I also blew a couple gauge bulbs earlier...just put new ones in, they seem pretty bright when I started it up today in the shop....
Help? Suggestions?
Jim

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1971 RT 1B
1971 RT 1B
1970 RT 1
1970 RT 1
1969 CT 1
1971 DT 1
1974 100MX
2016 BMW F700 GS
1982 Yamaha Towny
1971 CT 1
1975 DT400
Last Edit: by monel12.

Headlight keeps blowing out. 05 Feb 2018 13:54 #2

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Here is the service bulletin for wiring in a voltage regulator (if you decide to). It also lists 8 reasons why headlights can blow out.

www.yamaha-enduros.com/index.php/worksho...ulators/viewdocument
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Last Edit: by Devin.

Headlight keeps blowing out. 05 Feb 2018 13:55 #3

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Thanks, Devin.

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1971 RT 1B
1971 RT 1B
1970 RT 1
1970 RT 1
1969 CT 1
1971 DT 1
1974 100MX
2016 BMW F700 GS
1982 Yamaha Towny
1971 CT 1
1975 DT400

Headlight keeps blowing out. 05 Feb 2018 15:16 #4

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Geeez, there’s a new one on Fleabay, for $174.00!! Anything else I could use in place?
Jim

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1971 RT 1B
1971 RT 1B
1970 RT 1
1970 RT 1
1969 CT 1
1971 DT 1
1974 100MX
2016 BMW F700 GS
1982 Yamaha Towny
1971 CT 1
1975 DT400

Headlight keeps blowing out. 06 Feb 2018 02:36 #5

  • Hammer
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monel12,

As the headlight is AC, and produces prodigious amounts of current (hence the blowing bulbs), you may want to consider converting it to a 12 volt auto-type H4 bulb and a voltage regulator. It's a simple install, and I went with the adjustable voltage regulator which allows me some leeway in voltage. It's been documented here more than once, and should be easy to find with the search feature.

Hammer

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Headlight keeps blowing out. 06 Feb 2018 07:46 #6

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Thanks, I will look into that solution.
Jim

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1971 RT 1B
1971 RT 1B
1970 RT 1
1970 RT 1
1969 CT 1
1971 DT 1
1974 100MX
2016 BMW F700 GS
1982 Yamaha Towny
1971 CT 1
1975 DT400

Headlight keeps blowing out. 08 Feb 2018 02:34 #7

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monel12,

See my message to you!

Hammer

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"Who, More than Self, His Country Loved."

Headlight keeps blowing out. 08 Feb 2018 13:19 #8

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If it's a std system it sounds like the rectifier isn't working to soak off the excess to charge the battery. Another 'unlikely' possibility but unlikely in this case is if say it's designed for a 35/35 headlight & you went to a 15/15 it'll probably blow even with charging system working as lower wattage bulbs give brighter lights on an ac system. Don't think they make 15's in the large base bulb & i'm talking small bikes [old bikes]. Hook a regulator into the yellow from the mag or the blue after the switch in the headlamp?. [correct me if i'm wrong]. Any old single wire yamaha regulator will work. IT250 or any IT finned alloy ones are good.

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Headlight keeps blowing out. 08 Feb 2018 13:27 #9

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This one would do the job i'd think. Or go to the wreckers & might get a yamaha similar looking one for next to nothing.

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Headlight keeps blowing out. 08 Feb 2018 13:30 #10

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but double check anyway that the system is charging back to battery as that's quite possibly the main cause of the problem, except that a regulator will save your bulbs in a situation like this where the battery isn't soaking off the excess.

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