I always check the easy things first(FUSES) If fuses are all ok, check the plugs to see if your getting power to the door from the fuse box. If your not getting power to the plugs and the fuses are ok, then you will NEED TO CHASE THE WIRING HARNESS BACK TO THE FUSE PANEL LOOKING FOR BRAKES IN THE WIRE. Then next remove the front left master switch or the right side master switch from the door. If power is getting to the door, with a pick tool or a very small flat head screw driver remove the back panel on the switch and look over the circuit board. Check for burnt or corrosion marks. If the circuit board looks ok, Plug the switch back in with the circuit board exposed. Then with a test light find the + sign on the board and touch it with a test light to check if its getting power to the board. If your test light doesn't light up then its a bad switch.