Gosh, if it was working before than it HAS to be the wiring plug to the switch. since none of your heater speeds work, it has to be the wire feeding power in. You can use a meter or make up a little test jig with a auto lamp socket and working bulb. Hook one wire to any ground and use the other as a probe. Bulb will light when you touch a hot wire. You can poke into the connector. Just be sure you don't ever hit two at a time (if you do, it will just blow the fuse as a worst case and run the fan as a best case). If you find a wire that is hot (switch on, of course) you should be able to jump that wire to one of the others and hear the fan start up at some speed. That would indicate a switch failure - - not likely in your case. This is general knowledge based on only seeing the back of that panel one time. Most of the controls (sliders) are purely vacuum.