4-way Flashers not working

A known issue with the W20 chassis, that can affect some of your lights, is under the dash. There is a steel brace that supports the dash. This has a sharp/raw edge and there is a major wiring bundle that sits on top of this brace. After many miles of bouncing down the road, this can wear through the insulation on one or more wires and cause several different intermittent problems. Sometimes a fuse will blow, but not always. The contact made between a bare wire and the steel brace will vary if you hit a bump or jostle the dash when parked. The best solution is to put some type of a pad or cover on top of the steel brace so that it does not compromise the bundle of wires. It is easy to spot once you figure out how to stick your head under the dash and look around, which is not the easiest thing for most adults to accomplish. I doubt if this is your problem with the flashers but it is something to keep in mind. I suspect that your issue is with the flasher relay, especially if some of your lights were changed to LED's.