For 1988-1989 convertible models, first verify that the brake light comes on when you pull the emergency brake lever. The top control will not function if the e-brake is not pulled. If the light does not activate, either the emergency brake switch is dirty/broken and needs cleaned or replaced, or the bulb may simply be burnt out. If none of your idiot lights work (Charge, Fuel, Door, Low Coolant, etc), the clock/idiot light cluster itself may be broken, which is a completely separate issue. All the lights should turn on when the ignition is turned to On, before the engine is started, the Brake light being one of them, unless its bulb is burnt out.
Verify that the top control in the right-hand cluster switch (wipers, hazards, convertible top control) is operating correctly by checking continuity between pins as shown in the image below. Instructions for removing the wiper switch to perform this test are located here.