4 pin Trailer Lighting connector not working

If nothing is working I would check the ground first. The bare pin on the 4 way on the rig is the ground. All the positive pins are covered in rubber. You can also use a 12 volt test light or volt meter on the covered pins to see if you have voltage. Be sure the test light or meter has a good clean ground bolt or bare metal. One of the covered pins is running lights (usually brown wire) and the other two are left and right signal (usually green and yellow). When the brakes are applied both those wires are hot and when the signal is turned on one of them will then flash.

Try the running lights. If they work then the ground is good.