1968 CADI DeVILLE PART CONFUSION...

I am doing a full overhaul of my 68 cadillac coupe deville and after taking the dash apart...cleaning everything...and proceeding to put it back together...I realised that a part I took apart doesn't seem to go anywhere...
it is CLEAR plastic...(the whole piece)
it is in the shape of a 'J' with a small hook type lip...
it has a notch towards to hook end...
and the numbers on it are: 6458etc

It looks like it might conduct light (being clear) but I'm not sure.

any help would be GREATLY appreciated!!

thanks in advance