I have a 1979 Yamaha IT 175 that I am trying to put a brake light on. After looking at the light that is on it now, I see that there is an unused wire and that the bulb is already a dual filament. It looks like Yamaha used a tail light from a street legal machine but just wired up one filament for a tail light. I have a rear brake switch from an old bike that I want to put on. The bike has no battery and uses a lighting coil. The system is 6V. Would I just connect one end of the brake switch to the unused third wire on the tail light assembly and then splice the other side of the switch into the wire that feeds the tail light filament (from the lighting coil)? If so, I figure that would make both filaments turn on at the same time. I am not sure if the lighting coil would be strong enough to power the tail, brake, and headlight at the same time. Is there an easy way to make it so that when the brighter brake light filament goes on the lower watt tail light filament will go off? As you can tell, wiring isn't my thing! Thanks for any help on this.
Depends on how you want to switch your lights on and off. The voltage all starts in just one place - your stator. From there it divides out to different parts of the bike by switches. In your case a very basic setup can be just like you describe. Both bulb filaments are grounded through the bulb socket already because you have a working tail light. Tail light power can be routed through the brake light switch and back to the brake filament. This will work fine if there is NO light switch. If you have a light switch, take power from the input side so your brake light can work all the time (only your headlight and tail light will be turned on and off by the switch). The stator has limited output at idle. Your lights will dim when the brake light is on. A battery normally supplies the power at low RPM. You could add a small two pole relay that is triggered by the brake light switch. One pole would "break" the tail light power. The other pole would "make" the brake light power.
Strangely enough, what you said makes sense to me! I have some relays kicking around, but I think they are for 12 V. I will see what I have. There is a switch to turn off the lights (and a hi/lo switch) so I will be sure to take from the input side of that. I also have a small rechargeable 6V battery from a spot light. I was thinking of throwing that on the bike and using it for the brake light since it isn't on all the time. I could just recharge the battery as needed. This bike will mostly be on dirt roads and trails, so I am mostly looking to get it certified. Thanks for the ideas.
Something else to consider. In the 1970's GMC/Chev pickups had the front side marker lamps grounded through the "brake light" filament of the turn signal bulb. This made the side marker go out when the front turn signal was on. Thus you would get alternate flashing between the signal and the marker. For your application the tail light would be out when the brake light is on. +6v < tail light filament < +6V from brake light switch > brake light filament > ground When power comes from the brake light switch there is no longer any potential across the tail light filament and it stops illuminating. When the brake light switch is off, the tail light has potential because it is grounded through the brake light filament. This is simpler than using a relay, however if the brake light filament burns out, you have no rear lighting. Easier to understand with a sketch.
Ah, that's an interesting set up. That would serve me well, as I would rather have the tail light off when the brake light is on. Thanks for the idea. I will certainly look into that one as soon as the cold goes away. I need a heated garage!! :cry:
A bit more information. While the idea is sound, it won't work easily using a standard twin filament tail light bulb. This is because the bulb has both filaments joined internally for a common ground. It will work fine with separate bulbs since you can make the required connections externally. HOWEVER, we can view this a different way. By using the bulb socket shell (which is normally grounded) as the connection point for our brake switch voltage, we can get the desired result. The tail light pin would connect to +6V supply and the brake light pin would connect to ground. Of course anyone who tried to figure out your tail light wiring would be really confused. This type of reconnecting is possible as long as you have an isolated bulb socket. This means that the socket shell is not riveted to any metal part that connects to the bike frame (ground).
Thank God I didn't try any of this on my own! Those diagrams are a real help. I will take a closer look at the tail light assembly to see how things are connected. I just may post a pic of the set up if (and when) I get confused!
Here is a picture of the tail light. You can see that there are two wires to the bottom and one to the socket. The socket and backing plate that it is attached to is mounted in a rubber mount. This means that the ground wire to the socket is the only ground. The rest is isolated from the frame by the rubber mount. I just tried out what you said above and it works perfectly! Pull on the brake light switch and the tail light goes out and the brake light comes on. I am just having trouble trying to figure out why the tail light goes out once the brake light is on. Oh well, I am glad it works! Thanks again. =D>
You are most welcome. I was going to test it for you, but couldn't find the box that has all my leftover light bulbs. I've been tinkering with electrical stuff for years and I like projects like this. You've saved 3 entire candlepower (the brake filament is 21 candlepower). I had an ISDT Jawa with a 25W lighting coil. The lights were dim enough that I was almost invisible. Saved me a ticket one night, the cop couldn't see who was speeding. I heard a shout well after I passed the radar trap, but I just kept motoring along.
Stealth mode! I ride assuming I am invisible to the cars around me anyway, so this won't be much different. I never assume that people have seen my brake light. Like I said, my goal is certification and the brake light puts me one step closer.
