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 MANUALSFORD1987BRONCO 4.9 Y, STANDARD, T18REPAIR AND DIAGNOSIS (SINGLE PAGE)BRAKESTRACTION CONTROLANTI-LOCK BRAKE SYSTEMTESTINGYELLOW & RED LIGHTS ON STEADY OR INTERMITTENT
1987 Ford Bronco 4.9 Y, Standard, T18
Yellow & Red Lights On Steady Or Intermittent
1987 Ford Bronco 4.9 Y, Standard, T18SECTION Yellow & Red Lights On Steady Or Intermittent
- Check brake fluid level. Fill if necessary. If brake fluid is okay and lights are still on, ensure parking brake is not on. On models equipped with diesel engine, build vacuum up. If both lights goes off, replace isolator diode in wiring harness. Isolator diode is located in engine compartment by the left fender apron in the fluid level indicator wiring on master cylinder.
- Voltage at fluid level sensor should be 11-13 volts. If both lights are still on, temporarily ground diagnostic lead. If code 4 flashes, go to CODE 4 in this article. If any other code was flashed, replace computer module. If both lights stayed on, unplug connector from master cylinder switch. Connect a jumper wire between 2 Purple and White wires on connector.
- Turn ignition on. If both lights go off, check master cylinder switch connector. If okay, replace switch. If both lights stayed on, unplug computer module connector. Turn ignition on. If both lights go out, replace computer module. If Yellow light goes off and Red light stays on, check for short in brake warning light circuit. If okay, check ignition switch.
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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.