Well, you could start by replacing the light switch, eliminating that possibility right off.... but I fear that it may come down to wire chasing,... a tedious, but sometimes necesary task. Have you inspected the "cannon plug" where the whole harness passes through the firewall? Very often those slip fit connections corrode...
I'd reckon that the missing turn signal indicator light is a dead bulb... pul the instrument cluster out of the dash and install new bulbs in all the sockets, and check the contacts where the socket click in...
I'd reckon that the missing turn signal indicator light is a dead bulb... pul the instrument cluster out of the dash and install new bulbs in all the sockets, and check the contacts where the socket click in...