One way to find a short in the harness, and yes it is a PIA. Remove the bulbs from the lights. Check from the center at the bulb socket to ground. Should be open. If you have resistance you have something wrong. With all lights off. You can then look at each socket to ground at the same time. Should show less than 1 ohm. If that is all good then turn on one circuit at a time and see if you have voltage at the center of the socket. No lights in the circuit will keep the flasher from flashing. So just a steady voltage. I hope this helps. We had a less than family approved phrase for "ground loops" at work. We all hated them. When everything else is working then go back and take a good look at those four ways. If you like them get them working to.

Steve H