this might explain why you're having problems.
led's comes from the term "Light Emitting Diode". now the diode part of it is a check valve allowing current to only flow in one direction. if you wire them in the wrong polarity, they'll prevent current to pass through the led itself. polarity is very important when led's are concerned. led's also require less current than standard filament bulbs, so in order for them to flash properly a ballast resistor has to be used in line. it's not nearly as confusing as it might sound.