Also try the "wiggle test".
Reach under the wing and wiggle the wires going through to the light unit. Especially the black earth wire.on my '93 4/4 I had an intermittent/failing indicator and traced it to a poor earth connection. On dismantling I saw the earth wire pop rivetted to the lampholder and this was a loose fit. I had to drill out the rivet and repkace it. Bingo....indicator working again.
I had one of those once. On... off... on again... off again... on again... off again...
