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Once you follow Codewises advice and get it released, check the vacuum diaphram on the parking brake assembly. That is likely the cause of it not working. It should have vaccum supplied to the hose when in gear and the diaphram should hold vacuum. It is on the HVAC circuit so if it does not have or hold vacuum, I'd venture a guess that you are also having air delivery mode problems with the HVAC. Probably stuck in defrost mode.

This from the 1983 manual, but the parking brake should be the same for both cars.

Parking Brake Vacuum Diaphragm

Removal

1. Remove parking brake assembly as described.

2. Disconnect vacuum hose and remove one screw that retains diapraghm and bracket to parking brake assembly.

3. Detach link that connects cylinder to manual release lever and remove diaphragm.

Installation

1. Secure link to manual release lever.

2. Position diaphragm and bracket on parking brake assembly and secure with screw and connect vacuum hose.

3. Install parking brake assembly as described.

4. Test lock and automatic release operations with engine running in Neutral and Drive ranges. Parking brake should release in any drive range with engine running and should remain engaged in Neutral and Park with engine running and "brake" light should light with park brake applied and ignition in run position.