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 MANUALSFORD1985THUNDERBIRD BASE, 2.3 W, AUTOMATICREPAIR AND DIAGNOSISENGINE PERFORMANCETESTING & DIAGNOSIS1.6L & 2.3L EFI/TURBO TESTSTESTINGTEST FF - SHIFT INDICATOR LIGHT (SIL)
1985 Ford Thunderbird Base, 2.3 W, Automatic
Test Ff - Shift Indicator Light (SIL)
1985 Ford Thunderbird Base, 2.3 W, AutomaticSECTION Test Ff - Shift Indicator Light (SIL)
- Use only VOM/DVOM, not STAR tester, for this step. Turn key off and wait 10 seconds. Put transmission in Neutral. Set DVOM on 20-volt scale. Connect DVOM negative test lead to STO at SELF-TEST connector and positive test lead to positive battery terminal. Install a jumper wire between STI and signal return at SELF-TEST connector. Perform KEY ON/ENGINE OFF (KOEO) SELF-TEST PROCEDURE until end of CONTINUOUS SELF-TEST codes (DVOM reads zero volts). Depress and release throttle while watching DVOM reading. If reading did not change to a high voltage, depress throttle to WOT position and release. If STO voltage does not go to high reading, go to step 7). Leave test equipment hooked up. If reading changes to high voltage, remain in OUTPUT STATE CHECK and go to next step.
- Set DVOM on 20-volt scale. Connect DVOM positive test lead to battery positive terminal and negative test lead to pin 1 on dimmer relay. Depress and release throttle several times to cycle relay on and off. If relay does not cycle, go to step 5). If relay cycles, go to next step.
- Set DVOM on 20-volt scale. Connect DVOM positive test lead to battery positive terminal and negative test lead to pin 2 on dimmer relay. Depress and release throttle several times to cycle relay on and off. If relay does not cycle, remove jumper wire and replace dimmer relay. If relay does cycle, remove jumper wire and go to next step.
- Turn key off and wait 10 seconds. With DVOM set to 200-ohm scale, measure resistance between pin 2 of dimmer relay and SIL bulb. If reading is less than 5 ohms, replace SIL bulb. If reading is 5 ohms or more, repair open circuit in harness. Repeat QUICK TEST .
- Set DVOM on 20-volt scale. Connect DVOM positive test lead to battery positive terminal and negative test lead to SIL circuit of top gear switch. Depress and release throttle several times to cycle SIL circuit on and off. If SIL circuit cycles, repair open circuit in harness and repeat QUICK TEST . If SIL circuit does not cycle, go to next step.
- Set DVOM on 20 volt scale. Connect DVOM positive test lead to positive battery terminal and negative test lead to STO circuit of top gear switch. Depress and release throttle several times to cycle STO circuit on and off. If STO circuit cycles, replace top gear switch. If STO does not cycle, repair open circuit in harness and repeat QUICK TEST .
- Use only VOM/DVOM, not STAR tester, for this step. Turn key off and wait 10 seconds. Put transmission in top gear. Set DVOM on 20-volt scale. Connect DVOM negative test lead to STO at SELF-TEST connector and positive test lead to positive battery terminal. Install a jumper wire between STI and signal return at SELF-TEST connector. Perform KEY ON/ENGINE OFF (KOEO) SELF-TEST PROCEDURE until end of CONTINUOUS SELF-TEST codes (DVOM reads zero volts). Depress and release throttle while watching DVOM reading. If reading changed to high voltage, check SIL bulb and fuse No. 15. If bulb and fuse are good, repair short to ground in SIL circuit. If reading did not change to high voltage, go to TEST NN , step 13).
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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.