Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSMERCURY1991TRACER BASE, 4D SEDAN, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 121 (ENGINE CONTROLS - THEORY & OPERATION - EEC-IV 2.0L)COMPUTERIZED ENGINE CONTROLSINPUT DEVICESBRAKE ON/OFF (BOO) SWITCH
1991 Mercury Tracer Base, 4D Sedan, Automatic
Brake On/Off (BOO) Switch
1991 Mercury Tracer Base, 4D Sedan, AutomaticSECTION Brake On/Off (BOO) Switch
WARNING: This page is about a different car, the 1994 Ford Probe. However, it is still accessible from the selected car via links, so may be relevant.
BOO switch is wired to brakelight circuit. It signals the PCM when the brake is applied. The BOO input is used primarily by the torque converter clutch lock/unlock strategy.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.