If fuses and bulbs are fine then check the switch. Make sure that it is supplying the running lights with power when selected. If not, and you've got power coming into the switch, then you need a new one. If it IS sending power to the lights, then you'll need to trace the wires back and make sure they aren't broken. If the power wires aren't broken and you're getting power to the lights, then you'll need to chase down the ground.