WIRING NOTE:  This taillight has one 1157 bulb.  An 1157 bulb is an indexed two-filament bulb.  That means that it has two filaments of different sizes.  The brighter filament is wired to your turn signal and your brake.  The dimmer filament is wired to the running lights. There is no ground wire.  The bulb is grounded to your trailer body through the back plate.