The same exact thing happened to me... Start with the simple stuff. Check all the bulbs first. I just replaced them all (front and back). Then, check the fuses going to the lights. The flasher fuse usually works or doesn't, so if its working on one side and not the other that probably isn't the issue. Just in case, you may want to replace that, too. IMO
With me, it was a 3 stage issue. Once I replace all the bulbs the left directional would blink on the dash, but quickly. The right would work...sometimes lol so here is what I did after several posts and lots of advise from this board:
2. Check and clean all light grounds. I had headlight issues as well.(those grounds are located in the headlight housing) The turn signal grounds are in front of the radiator . Remove the screws, sand down and clean all contact areas. Put a dab of diode grease on the metal and screw back in. I also added a 10 gauge ground wire to all the grounds (including the headlights)
3. Disconnect the connectors to the directionals (4 pin - white). Just follow the wire harness from the directionals. Spray them down with contact cleaner. Then dab some grease and re-connect.
My problem ended up going one step further. The connectors, although they looked clean, were corroded. I cut out the connectors altogether and made my own with individual covered connectors.
NOW, all my lights work perfectly all the time. It was an issue that was driving me nuts for over a year! Take all these steps in that order, and you should be ok.
If you need any further assistance I'd be more than happy to post some pics to show you specifics. You can also feel free to PM me directly. I know how frustrating that light issue can be. Good luck! - Eric
A turn signal flasher will only flash when current is running through it. So, if a bulb is blown, ground bad, or connecter corroded, the current flow will be insufficient to operate the flasher. So even if just your right front bulb is blown (say) the right rear and indicator won't function.
It is also possible that the contacts in your switch have become flakey. Try wiggling the lever when it's in the right position, and see if that produces any results. But, it's more likely that your problem is one of the issues ericb214 suggested.