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Yam DT50 headlight problem


Guest Avro730
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Hi, My sons Yamaha DT50 headlight is useless, might just as well use my lighter for the all the good it is. Have changed bulb, no difference, swapped the bulb to a different bike and works fine in that. Have been told that in the lighting circuit there is a resistor(I think that's what he said?) which can fail and then resist too much (I guess) causing weak headlight. have checked battery 13v off and 14.5v when running, but only 1.3v at the headlight when running, at best. Only electrics I can find aside from the actual wiring is a sealed unit under the seat. . I am located in SW France and most bike shops/dealers are not exactly user friendly and parts take an age to arrive, if ever. Any help appreciated, could use a wiring diagram if anyone knows of one online.

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Have you checked all the connections to make sure they're a tight fit? Also if you have plug connectors check the pins inside for corrosion because it sounds like a poor connection to me. If they are corroded then remove the plug part and get some sand paper and rub the pins down until they're nice and shiney again a bit of WD40 maybe speed up the process as well.


Good luck!

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:stupid:

Yeah.....I've not heard of resistors in lighting circuits before..... :?


But Adam is right.....I suspect there's a high resistance connection somewhere in the lighting circuit.....or the earth connection from the headlamp is corroded and gone high resistance......and also check the handlebar switches.....make sure they're all clean and making good contact..... :wink:

I tried searching for a DT50 wiring diagram....but the only one I found online was pretty illegible......dunno if there's a Haynes manual available for that bike?..... :wink:

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Bob....couldn't be a zener gone open circuit can it?....

I wouldn't have thought so Derek.......the zener (if it has one) would be across the circuit rather than in line and shunts the excess voltage......so if a zener went open circuit you'd get a higher voltage as it wouldn't be limited..... :)

Now....I did have a zener go short circuit on my old Bonneville......whilst I wa doing 70 (and a bit) in the outside lane of the A2 in Kent many years back......that was interesting as it took the main fuse out......so instant loss of power...... :shock: Clutch in and coast to the hard shoulder.....across 2 lanes of fairly quick moving traffic.....not recommended..... :wink:

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power the headlamp directly from the battery. that way you'll see if it just rubbish or if there is something highly resistive in the circuit like a bad connection or crap wire.


you can remove the whole headlamp to tdo this or use jump leads direct from your battery to the bulb wiries. be careful tho and an assistant might be useful etc etc.

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Hi all. Thanks for the responses. I did find a slight amount of corrosion on one of the pins in the "black box" inder the seat, cleaned it but made no difference. I will try the direct to battery test and I suspect that there is a bad connection somewhere, but like all of these the things it seems that the wiring loom is sealed in plastic so cant even see where any connections are let alone see if they are good. BTY there are no switches as the light is on all the time the engine is running and there is no "dip" switch (only on swiss models according to the hadbook) This is a French market model.


Stay tuned for further transmissions!

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Mystery solved! Having spent ages looking at the headlight assembly (looking but not actually seeing) I gave up and went and fixed the lights on my bike trailer. Whilst doing that I was looking at the bulbs in the trailer which has the combined twin filament brake/rear type bulbs. It dawned on me that the Yam headlight had twin filaments as well. Rember I said that the bike dosent have a dip switch (only the Swiss model has a dipping headlight), so why have a twin filament bulb? Obvious answer is that there are millions of bulbs and bikes that do have a dip setting so they have just used a standard part. With me so far?


So on inspecting the Yam headlight I noticed that the bulb holder (standard part) has three feeds a common, one for dip and one for full beam. Problem was that the tab for the common was broken off and the wires (only two as it has no dip) were connected to the dip and full beam tab (but not the common) I can only guess that some numpty at some point broke the common tab and then connected the "spare" wire to the dip connection. The result was it worked, sort of, but very weak.


Have now fitted new bulb holder and connected wires correctly and hey presto there is light and lots of it.


Many thanks to those who took the time to send advice


Happy night riding now.


Dave, in not so darkest France

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Mystery solved! Having spent ages looking at the headlight assembly (looking but not actually seeing) I gave up and went and fixed the lights on my bike trailer. Whilst doing that I was looking at the bulbs in the trailer which has the combined twin filament brake/rear type bulbs. It dawned on me that the Yam headlight had twin filaments as well. Rember I said that the bike dosent have a dip switch (only the Swiss model has a dipping headlight), so why have a twin filament bulb? Obvious answer is that there are millions of bulbs and bikes that do have a dip setting so they have just used a standard part. With me so far?


So on inspecting the Yam headlight I noticed that the bulb holder (standard part) has three feeds a common, one for dip and one for full beam. Problem was that the tab for the common was broken off and the wires (only two as it has no dip) were connected to the dip and full beam tab (but not the common) I can only guess that some numpty at some point broke the common tab and then connected the "spare" wire to the dip connection. The result was it worked, sort of, but very weak.


Have now fitted new bulb holder and connected wires correctly and hey presto there is light and lots of it.


Many thanks to those who took the time to send advice


Happy night riding now.


Dave, in not so darkest France

Nice one well done and saved a few bob in the process

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