If you are referring to the "brake/turn"lamp and the lamp is an LED. Maybe the LED's do not draw enough current to allow a traditional flasher-tube to work properly.
Some vendors offer solutions for this problem (this reality?) in the way of resistors and/or
an updated flasher (for 12v lamps, I do not know if a 6v LED bulb flasher is available for use with 6v LED lamps).
On my 6v positive-ground COE, I plan to place a 6v-12v converter under the dash and use 12v LED bulbs and a 12v LED flasher.
