e-mail me a picture of your turn signal unit, or post it here. Is it the more modern 3 arm black plastic version? If so, then the connections are all made by the switch itself and use the same wires, the flasher lever just connects all together so it is most likely a bad connection inside the turn signal unit itself. The "trailer box" isn also a culprit, but you've changed that already and ti doesn't know the difference from turn and hazard so if rear turns work and hazards do not, then you know the box is good and that leads back to the switch.