Can you hear a rapid clicking at all? If so it will be the hazard light switch as it doesn't get mush use coupled with the switch being old the beeswax used inside dries up and so the contact isn't good, you can take it apart to clean or just get a new switch, this effects indicators as well as all power goes through this switch.

If nothing at all then I would be checking the flasher unit/relay, or the power feed.

Martin