ahilis

Found the problem. It wasn't wire gauge alone. The original designer of the headlamp circuit for the DT series used a combination headlamp switch which has three switches in one. The headlamp runs on AC straight from the magneto, through one of the three throws, unregulated or rectified, and it is supposed to be the only thing running on that AC output from the magneto. (The 6V rectifier/regulator runs on a different output from the magneto altogether.) The taillight runs through one of the other two of the three switches, since it's power comes from the 6VDC through the battery like the whole rest of the bike. Well, someone sometime somewhere at Yamaha decided they would omit some of the wiring in the wiring harnesses of this bike. They decided to use only one of the three throws of the headlamp combination switch and combine the output to the headlight and the output to the taillight. Now the taillight, headlight, and instrument lights are all on the 6VAC output from the magneto, not just the headlamp. The other two throws on the combination switch are unused and the wires are literally missing from the loom. So what happens when a person puts on the brake light? The taillight and brake light are the same bulb with the same earth. Now one filament in being powered by +/- 6VAC from the magneto whilst the other filament is being powered by +/- 6VDC. Not only do the voltages not match at any given time, but one is AC and the other is DC AND now the headlamp's current is travelling back and forth across the bike and through all the circuits instead of having it's own path to earth. The headlamp goes so dim that you can hardly see where you're going. The same thing happens whilst using your indicators; so now, if you're riding at night, not only does your headlamp nearly go out every time you use your brakes, but you must now choose between using your indicators to signal your turn to other drivers or being able to see where you're going. The fix was very simple. I added only one wire, which was from the ignition switch positive output to the throw on the combination switch which was intended to power the taillight circuit, as per the wiring diagram, and moved the pins in the wire harness connectors around so that the taillight circuit comes from the output of that switch...as per the wiring diagram. Painfully simple, yet now my headlamp burns brighter than ever before and neither the brake light nor indicators affect it's brightness. The taillight and instrument lights burn much brighter and are more consistent since it has the capacitance of the battery, increasing visibility to other drivers, especially at lower engine speeds. I have no way to verify this, but it seems like there is a little extra power from the engine as well...either from more current being available to the igniter or from less current being drawn from the magneto or both. As a matter of fact, the engine RPM used to drop slightly when you switched the headlamp on at idle speed, where as now it seems to have no effect. Anyway, just thought I'd let you all know before you take the time to reply to my original post. I will be sending a formal complaint to Yamaha because this lighting problem was so extreme that it was quite unsafe. Keep well!

The bike is a brand new DT175 from Yamaha South Africa. I desperately need to change my headlamp housing and the one of choice uses an H4 bulb. I am battling to find a 6V H4 35/35 headlamp globe in my area. I have just seen them on http://www.norbsa02.freeuk.com/goffybulbs.htm , so I know they exist now. However, I have measured the AC output of my magneto and I'm getting around 6VAC on the leg feeding the 6V headlight and 12VAC (13.5VAC max) on the leg feeding the 6VDC rectifier/regulator. Could I simpy run a 12V bulb on the 12VAC leg, in parallel with the rectifier/regulator, eliminating the need for the 6VAC output? Even a 60-watt 12V bulb would draw less than my 6V 35-watt bulb, so unless each of these two outputs from the magneto has it's own maximum current, it should work out nicely. I'd be getting a much brighter bulb and drawing less from the magneto. This would let me run a 12V headlamp bulb, which I could replace quite easily from any auto spares shop, and keep the rest of the system 6V. The cost would be nothing. But will it work? I've heard of others replacing their 6V regulator/rectifier with one from a 12V bike, then switching all thier bulbs to 12V bulbs and letting their horn be louder. I don't have a wiring diagram for this bike, so I'm not able to tell if my igniter/coil runs on 6VDC from the battery of if it's selfcontained, getting it's power straight from the magneto...which would mean I wouldn't have to mess with that. Anyway, thanks for any insight on the matter and keep well!

Yeah, all of those signs are because of the battery. They poop out every now and then, even with proper water levels, and then your indicators won't work unless your RPM is high enough, etc. I found my problem. Someone at Yamaha decided to rewire the bike. They left all the same switches and connectors, which normally isolate the taillight and everything else from the headlight, but omitted some of the wiring and joined others to compensate. Now everything on the whole bike is tied together and they don't work well when everything is on, like when making a turn. Fortunately, since the same switches and harnesses were used, I can just add a couple of the missing wires and be done with it. Thanks and keep well!

I just bought a DT175 in Botswana. The bike comes from Yamaha South Africa. The headlamp dims so much when I apply the brakes, regaurdless of speed/rpm, that I can hardly see where I'm going. If I use my indicators, it does the same thing and when I use both, the light almost goes out. I managed to measure, with no other lights on, a 50 mV voltage loss on the negative side of the bulb and 450mV on the positive, making me suspect that the earth is good and they should have simply used heavier guage wiring from the factory. I would like to change the 165mm x 100mm headlamp with a standard, e-code headlamp housing anyway, which would require a different bulb base like the p43t of an H4. This means that unless I can find an H4 in 6V, if they even exist, I might have to attempt a 12v conversion. I'd get less voltage drop, but unless there is a more robust stator that will fit this bike I might not get much of a charge on the battery below about 3000rpm. Otherwise, if I can find a 6V H4, I will just work out heavier guage wiring where it's needed and use 6V H4 globes. That would raise another question: anyone know how much current this magneto is able to produce? And is the headlamp circuit completely separate from the rest of the lighting system? Thanks for any insight on these matters! Keep well!

I just bought a DT175 in Botswana. The bike comes from Yamaha South Africa. The headlamp dims so much when I apply the brakes, regaurdless of speed/rpm, that I can hardly see where I'm going. If I use my indicators, it does the same thing and when I use both, the light almost goes out. I managed to measure, with no other lights on, a 50 mV voltage loss on the negative side of the bulb and 450mV on the positive, making me suspect that the earth is good and they should have simply used heavier guage wiring from the factory. I would like to change the 165mm x 100mm headlamp with a standard, e-code headlamp housing anyway, which would require a different bulb base like the p43t of an H4. This means that unless I can find an H4 in 6V, if they even exist, I might have to attempt a 12v conversion. I'd get less voltage drop, but unless there is a more robust stator that will fit this bike I might not get much of a charge on the battery below about 3000rpm. Otherwise, if I can find a 6V H4, I will just work out heavier guage wiring where it's needed and use 6V H4 globes. That would raise another question: anyone know how much current this magneto is able to produce? Thanks for any insight on these matters! Keep well!

I'm assuming all your questions have been answered since this post is nearly a year old. I have just purchased a new DT175 and have had the same experience in finding neutral...a light tap from second is easier than finding it in first. 10 years ago, I had a DT180, which I think was a 1992 model, with about 35,000km on it and it was the same. And they do lurch forward a little when going from N to 1st, especially when they're cold. If the idle speed is anything less than spec, it stalls the engine. But I have a question for you...I'm just trying to find a little history on the DT175. Do they still sell them in the UK? I bought mine in Botswana, and it originated in South Africa. I've only had it a month, so I'm sure it's a 2007 model, not 2008. I'm assuming that South Africa is the only country left to sell these bikes. I'm not even sure when, from the time it came out in the 70s, it changed into what it is today. My '92 DT180, Brazillian made but same bike, looked just like this one and I'm assuming yours does too. Do you have problems with your headlamp dimming to the point that it's useless when you use your indicators and/or brake light at night? I have to choose between using my indicator and being able to see where I'm going when I make a turn in the dark. Cheers!