Do the cheap easy things first:
-check and/or ad ground connections
-check flasher unit on fuse panel
Then read this (and note the hint to do the wiring from the column before committing to steering wheel removal).
On my Dad's old work trucks the blinker units could get bonked by your left foot. Sometimes the fuse panels would get cracked if aggressive people in work boots got in there. I recall one truck where I would have to gently apply pressure to the blinker unit with my foot while driving if I wanted signals. Eventually that got fixed...