The indicator lights are actuated by the same circuit that activates the turn signals at all four corners. First remove the connector on the back of the dash cluster. Activate the turn signals. Test with a 12 volt test light the wires on the connector. The known good one will light, and the other either will or won't. If it will, there is a problem in your cluster wiring. If not, there is a problem downstream in the harness that connects to the cluster, or even farther down the line. I can't remember what color the signal wires are so trace the printed circuit from the bulbs to the connector.