This is really a John Reagan question but I thought it might be of general interest. We just installed a Fun Projects stoplight switch on a 1911 T. No problems with the installation and it works fine on 12 volts. We would like to use the magneto to operate the brake light. Will the higher voltage from the mag damage the Fun Projects switch?
It will handle it no problem. The light bulb needs to be a 9 volt bulb.
Will a single 9v bulb hold up to full magneto voltage? Magneto headlights were wired in series. Not sure what voltage the bulbs were, but the voltage was split between the two of them. I would think mag voltage to a single 9v bulb would blow it in short order. What am I missing?
Royce just may be right! If you are using the mag to drive a stop light the engine is usually slowing down or close to idle when the brake is applied meaning lower voltage from the mag. A lower voltage bulb would be brighter which is what you need for a stop light.
Problem with just a 9V bulb is if you do an emergency stop with the foot brake while the engine is at full revs. Not only will the bulb be blown in the blink of an eye, but if the engine stalls because of stamping on the brake pedal without holding down the low halfway, as can happen in a panic, it's not going to work either.
It's a novel idea that would work in the ideal world where we always come to a gradual controlled stop, but best thing is to run it from a battery.
The switch can handle it but because the stop light is so important I sure would want it to be bright and always work. What if your engine quit and you had to make a sudden stop as a result. A stop light is a safety item that you really need to work for sure every time - period.
Thanks John and others for answer to my question about the Fun Projects.
I have used the magneto on my 13 T to power a Stoplight for thousands of miles. I use a modified socket with an 1157 light bulb for the Stoplight. In 6 or 7000 miles of all manner of driving I have replaced the bulb once. 1157 bulbs are cheap and easy to find at a parts store. I like the magneto powered stoplight because it works even with a discharged battery. It also gives a nice bright light that is easy to see.