Possible wiring problem on '73 1 ton dually

[Phantom_Lord]

Hey guys, I need a little help with a project. I was given a 1973 quad cab dually, but it needs a bit of work to fix up. Most of it shouldn't be too terribly hard, but I'm a little stumped with one thing. My blinkers, hazards, brake lights, and tail lights all don't work. I've checked all the fuses and flasher units and they all seem to be fine. I replaced most of the fuses anyway, just to be sure. What was really weird was the fact that to begin with, the front driver's side blinkers worked occasionally, and after I replaced the fuses, I managed to get the back driver's side blinker to do the same. Now neither works at all. All the bulbs seem to be in good condition, so I'm thinking that it's some kind of wiring problem. I would like to get this problem fixed before I worry about doing the rest. The truck runs, though the spark plugs and wires need to be replaced, and the timing is off by quite a bit. The previous owners parked it in a wrecking yard and it sat there for years. The truck is actually pretty nice, the body and the interior both look decent. If anybody could give me any ideas on what to do, I would really appreciate it.