brake lights came on parked car, why & what do I do? on 1990 Toyota Tercel

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My car was parked in the driveway & brake/tail lights came on. Why, and what do I do about it? What can I expect to pay for the repair.
(2) Answers
Are all three brake lights on? You probably have a failed brake light switch, $30.00-$75.00. If it's just parking lights on (should be both rear and front) then it should be properly diagnosed , may be several things causing it , one of which would be the headlight (combination) switch. Don't guess , that can make it much more expensive than needed . Diagnosis could be up to 1 hour labor , depending on the fault and location of it.