I don't know about a 140 but on older cars, the problem is usually the emergency flasher switch. Turn the emergency switch on and off about 10 times and then try the turn signals. If it doesn't work, try again but this time leave the switch in the emergency position and see of all the turn signal lights work on both sides. If not, fix the ones that don't work. Then try again.
If this doesn't work, I'm sorry. It has worked on both my 84 126 and 91 124.

Paul

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84 500 SEL (307,xxx miles)