do you have a voltmeter? Voltage=current*resistance measure the voltage from ground wire to running light wire, then turn the bike off and measure the resistance from the battery to the running light. solve the equation and you have your current. use the current and make your voltage number like half or so, then solve again for your new resistance. subtract your original resistance from the new value and then take a trip to radio shack or just use digikey.com to buy your new resistor. then you have to solder that resistor inline with the running lights so they will be in series.