I saw this question on another forum and thought maybe it would be worth posting here. I don't recall this being covered here before.
If anyone is having trouble with front or rear signals on a 64 or 65 Acadian, there's a good chance it's the switch and it's repairable without buying a new one.
This is how the switch looks-
And this is what you see when you remove the white "horseshoe". The brass squiggly contact strip and brass pins (Index finger pointing to that area) were dirty on mine. I cleaned them up with fine sandpaper, a couple of tweaks on the brass strip to make sure the contact on the pins was firm enough, and it worked fine after that.
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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles
1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)