The brake light on the dash? I would guess it's because the switch on the proportioning valve has gone off-center...have you had the brakes worked on or bled lately? I would take the wire off the switch (it's on the firewall on the driverside near the hood hinge on my '67) and see if the light goes out...
The switch is set to turn the light on if the proportioning valve (I may be referencing the part incorrectly, but it's the same assembly) detects lower presser on the front or rear brake circuit.
You might check the wire going to the parking brake assembly to make sure it's not grounding out. If it's not an XR-7 the light on the dash would come on,I believe on a car with an overhead console it would show up there instead. Good Luck
The only brake light that is directly associated with the emergency brake is the OPTIONAL one (I think it was in the lighting option group, actually) that is a large one that is on the lower dash just near the emergency brake handle.
On cars so equipped, it has a little switch that detects if the handle is not pushed in all the way, and if it sees that it's not (i.e., it decides that the emergency brake is on) - it flashes the warning light - trying to get your attention before you burn off your brake shoes *L*
I'm pretty sure if the brake light on the dash is only connected to the proportioning valve switch (see the other brake light thread in this group for a detailed, blah-blah-blah, boring discussion submitted by one of our members who thinks he knows it all, but is really a huge, break-it-or-accidentally-fix-it garage warrior.
'course - this is info learned from books and from personal experience with my '67 standard - I could be completely off base for the RX7...in which case, I NEVER SAID THAT!!!