The 1974 Coupe deVille is equipped with automatic seat back release locks.
They are actuated by big solenoids which are mounted in the back rest of each front seat.
When you open the door they are actuated, and the seat backs can be folded forwards to allow access to the backseats without having to manually unlock the seat. You can hear this "Automatic Seat Back Release" working when you open or close the according door.
It worked perfectly on the passenger side, and most of the time on the driver side.
When the door was open though you could sometimes hear a rattling sound from the solenoid as it did not make good contact.
That was not acceptable for my standards of course.
You have to remove most of the back seat material to get to the solenoid unfortunately.
Once we got it out, we took the solenoid apart. Some of the actuators insulation foam had crumbled inside the end stop of the solenoid - so we replaced that, cleaned and lubricated everything, and put it back together.
Unfortunately the problem was still there after this.
So we eventually found out that the striker where the seat latches, was not adjusted correctly. Something must have gone wrong at the factory already.
We had to modify it slightly to make it perfect again, so that the solenoid could disengage itself properly when the seat back was in the back position.
When everything was back together it worked for a while before it broke again. I will have to find a good working solenoid now and replace it once again.UPDATE
: You can read about the final repair here!
You have to remove the seat back material to be able to access the solenoid and latch mechanism
The latch mechanism
The solenoid disassembled - before cleaning - there are two coils inside.
A quick drawing of how the system works.