[5th_bike]

You could diagnose it by looking at the wiring diagram (p. 206 of the service manual) and finding the turn signal wiring. It's a light blue, a blue, and a light green wire. Then, undo the connector that the wiring goes through. Most likely, it is underneath the tank and you may have to take the tank off (a piece of cake, just don't leave the petcock on 'prime', and also undo the vacuum tube behind the petcock).

It is kind of weird that both turn signals are giving out, this makes me suspect that it is not the switch, but maybe an unreliable connection elsewhere, maybe at the connector I mentioned above, or at the turn signal relay. Try undoing that connector, and reconnecting it, and then try your turn signals, if they work fine, you're done. Switch power 'on' for just the time needed to test.

It the turn signals are still flaky, power off, undo the connector again, and with a multimeter, test the wiring to your switch for continuity in all (two) positions, left and right, i.e. test light blue (common) wire vs. blue (left) wire, and light green (right) wire, respectively. If continuity is flaky in both directions, it's the light blue wire, or the switch. If continuity is good, it's elsewhere in the circuit - maybe the light blue wire from the turn signal relay to the connector, or maybe the orange/green wire to the relay.

If your riding lights (the 'little' lights in both front turn signals) have no problems, it is not a ground wire (from the lights to ground) issue.