electrical, CHMBL works all other brake lamps do not

The turn signal switch IS the multifunction switch. The center brake light circuit comes right from the brake light switch, but the side brake light circuits go through the signal switch so it can break the connection to the brake light switch and connect it to the signal flasher. Assuming your brake light and signal light are one and the same bulb, your observation that the signals work would prove the wiring to the bulbs is okay. That just leaves the signal switch and the terminal in the connector. Before you replace the switch, check the terminals to be sure none are black from being overheated, and the connector body isn't melted.

ok thank you caradiodoc!
To clarify: for the Caprice ( and perhaps most American vehicles) the location of the turn signal switch ( multifunction switch) is in the steering column - in other words the turn signal lever (includes the cruise, windshield wiper functions, high beam) is part of and /or connected (by way of the lever) to the turn signal switch (multifunction switch). To access this switch please confirm the steering wheel must be removed.

I never did one on your car model but by the early '90s most multifunction switches were held on with two or three screws on the side of the column and it wasn't necessary to remove the steering wheel. Most require removal of a few screws from the bottom to separate the two halves of the steering column cover.