Did you solve the problem?

I have similar problem from tonight.

When the headlamps are off,
all turn signals work fine with the usual audible click.

When the headlamps are on,
left turn signals are steadily on at max brightness. The left-pointing green arrow is also steadily on. They do not blink even when push down the turn signal lever.
When I push up the turn signal lever, right turn signals and right-pointing green arrow blink, the left turn signals and left-pointing green arrow are steadily on, and there is no audible click sound or the click sound is of low loudness.

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1992 300D 2.5 turbo diesel. 319 k miles.
124.128 chassis, 602.962 engine, 722.418 tranny.