My 76 Malibu uses an 1157 dual filament bulb for the rear turn signal bulb. The one on the left (drivers side) works fine. The bulb on the rear right will light but not flash. The 4 way hazard flashers work. The bulbs second filament lights when when I engage the headlights. I have replaced both the front and rear bulbs and cleaned the bulb sockets. I have replaced the only turn signal flasher that I know of located in the fuse panel. There are 2 other units that look like flasher relays among the wiring under the dash. Don't know what they are. One has a noticeably longer case than the other. Not sure where to go at this point. Should I pull these two other units and try to track down what they are by the numbering stamped on them?