If your hazards work but turn signals don't, you at least know the wiring under the truck is working. I'd lean towards it being the switch or the wiring right around it, but you never know where electrical gremlins are going to get into. There are two plugs coming off the switch, one for high/low beams and one for the turn signals. The horn wiring is tucked in with one of them too. All told you'll have three wire bundles coming down the column when you add in the hazard switch. Check em all.
The reverse lights usually end up being the switch or the bulb/socket. The reverse light socket seems to gather a lot more moisture than the turn or tail lights for some reason, so even with new bulbs it may be that is the source of your trouble. The only way to really check is with an ohm meter on the contacts to the light rear assemblies. If you get continuity then the bulbs are getting a connection. The switch you can short closed under the truck on the trans, it is the one further back, almost to the tailshaft. You can just unplug it and plug the wires together. Reverse lights should come on when the key is on. If they were working though and just stopped at the same time the turn signals went then it could be a common cause but it seems sort of unlikely to me.
Wiring issues can get very strange. On my old 79 I had wiring for the reverse lamps get shorted in the harness to the main alternator wire. (it had gotten hot at some point and melted things) The result was the truck would not die when you turned off the key. Power was running back from that short to the reverse light wiring and powering the coil and fuel pump just like the key was still on. I took a wild guess that I had a short and ended up pulling the entire harness apart. Needless to say I was thrilled to find my problem within the first 4-5 feet.

My parting tip, just another "what he said": When in doubt ground something.