QuestionI have recently bought a honda cg125 but the stop/tail light won't work. Everytime I put in a 6v stop/tail bulb it blows after a couple minutes, and it seems impossible to get the recommended 3/10w bulb (recommended by manual). Can I use a different bulb (the ones that blew were 6v 21/7 watt bulbs) or is there anything at all I can do?
Please help.
AnswerBulbs blowing like this are usually caused by one of two problems: the voltage is too high or the ground is intermittent.
If all the other lights are working as they should it is not likely that the voltage at the tail light could be high enough to damage the bulb, but it wouldn't hurt to put a voltmeter across it to eliminate that possibility.
Assuming that the voltage is 7V or lower when the engine is running at about the RPM it would on the road, stop the engine and move the wires from the tail light assembly around to see if you can make the light blink or turn off by moving them. If you can, figure out which wire is doing it and you have solved the problem (it will probably be the green one).
If that doesn't work, have a good look at where the green wire from the tail light plugs into the wiring harness and where it connects to the bulb socket inside the tail light assembly. Also look at the inside of the bulb socket. Any corrosion in the bulb socket should be cleaned out thoroughly. Corroded connectors should be replaced with new bullet connectors (auto parts). If the problem is the connection between the wire and the socket it may be possible to solder a new wire to the side of the socket, but be careful not to melt any plastic parts when you heat it up.
There is another slim possibility that comes to mind: I couldn't find a good schematic for the CG125, but I did find one for a similar vintage CB125 and from what I can tell they do not have voltage regulators - the voltage is regulated entirely by the battery and the lighting load. This was not uncommon in those days, particularly on biked that were built to sell for low prices. I have heard of people converting bikes with this type of system from their original 6V to 12V by simply changing the battery & bulbs (a 12V ignition coil would probably be a good idea too).
If your bike has a 12V battery, putting a 12V bulb in the tail light should cure the problem.
As for where to get the bulb, Unfortunately, these days most of the parts people only know how to look up which bulb the manufacturur specified for the vehicles in their database and not by bulb specification. It is possible that your local auto parts dealer has what you need but doesn't know what it actually is.
I would start by downloading the GE automotive bulbs catalog and looking in there for a part number http://www.gelighting.com/na/business_lighting/education_resources/literature_li...
You could also try places that sell parts for restorers of antique vehicles.
