Diagnostic Aids

Perform this test only when directed here by a driveability symptom. This test is only intended to diagnose:

Wiring harness circuits (SIL).
Top gear switch.
SIL dimmer relay.
SIL bulb and SIL circuit fuse.
ECA.

Fig 1: Shift Indicator Light (SIL) Circuits (1.9L)

Fig 2: Shift Indicator Light (SIL) Circuits (2.3L HSC)

1) Check SIL Operation On Thunderbird 3.8L SC, go to step 18). On Escort, Tempo, Topaz and Tracer, inspect SIL while driving vehicle. SIL should turn on when optimum-shift RPM for each gear is reached. Light should be off in top gear. If SIL light is always on, check for short to ground in SIL circuit. If light is always off, check for open in SIL circuit. If light is always on, go to step 10) (Escort and Tracer) or step 6) (Tempo and Topaz). If light is not always on, go to step 2).

2) Check SIL Circuit Fuse Turn ignition off. Remove and inspect SIL fuse. If fuse is okay, go to step 3). Replace fuse if blown. If fuse blows again, repair short to ground between fuse and SIL bulb. Check SIL operation.

3) Check SIL Bulb Turn ignition off. Remove and inspect SIL bulb. If bulb is okay, go to step 15) (Escort and Tracer) or step 4) (Tempo and Topaz). If bulb burned out, replace bulb and check SIL operation.

4) Check Continuity Of SIL Dimmer Relay Turn ignition off. Disconnect SIL dimmer relay. Set DVOM on 200-ohm scale. Measure resistance between pins No. 3 and 5 on SIL dimmer relay. If resistance is less than 5 ohms, go to step 5). If resistance is 5 ohms or more, replace SIL dimmer relay.

5) Check SIL Dimmer Relay Function Turn ignition off. Apply 12 volts across pins No. 1 and 2 of SIL dimmer relay. Set DVOM on 200-ohm scale. Measure resistance between pins No. 3 and 5 on SIL dimmer relay. If resistance is not 40-55 ohms, replace SIL dimmer relay. If resistance is 40-55 ohms, go to step 6).

6) Check Voltage At SIL Dimmer Relay Turn ignition on. Set DVOM on 20-volt scale. Measure voltage between test pin No. 5 of SIL dimmer relay wiring harness connector and negative battery terminal. If voltage is more than 5 volts, reconnect relay and go to step 7). If voltage is 5 volts or less, repair circuit between SIL fuse and SIL dimmer relay.

7) Check Voltage At Top Gear Switch Turn ignition on. Disconnect top gear switch. Measure voltage between SIL dimmer relay side of top gear switch wiring harness connector and negative battery terminal. If voltage is more than 5 volts, go to step 8). If voltage is 5 volts or less, repair circuit between top gear switch and dimmer relay.

8) Check Operation Of Top Gear Switch Turn ignition off. Disconnect top gear switch. Set DVOM on 200-ohm scale. Measure resistance of top gear switch while shifting transmission from highest gear to next lower gear. If circuit does not open and close, replace switch. If switch opens and closes, go to step 9).

9) Check Continuity Of SIL Circuit Turn ignition off. Disconnect top gear switch. Disconnect 60-pin ECA connector. Inspect terminals, and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving ECA disconnected. Set DVOM on 200-ohm scale. Measure resistance between test pin No. 53 and ECA side of top gear switch vehicle harness connector. If resistance is 5 ohms or less, go to step 10). If resistance is more than 5 ohms, repair open circuit between top gear switch and ECA. Reconnect all components, and verify operation of SIL.

10) Check SIL Circuit For Short To Ground Turn ignition off. Put transmission in high gear. Set DVOM on 200-k/ohm scale. Measure resistance between test pins No. 53 and 60 at breakout box. If resistance is 10,000 ohms or less, repair short between top gear switch and ECA. If resistance is more than 10,000 ohms, replace ECA and repeat QUICK TEST .

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 10) to step 15). No test procedures have been omitted.

15) Check For Voltage To SIL Socket Turn ignition off. Remove SIL bulb. Place transmission in any gear except top gear. Set DVOM on 20-volt scale. Turn ignition on. Measure voltage between power contact at SIL socket and chassis ground. If voltage is more than 10.5 volts, go to step 17). If voltage is 10.5 volts or less, connect SIL bulb. Go to step 16).

16) Check Operation Of Top Gear Switch Top gear switch is normally closed and should only be open when vehicle is shifted into top gear. Turn ignition off. Disconnect top gear switch. Place transmission in any gear except top gear. Set DVOM on 200-ohm scale. Measure resistance of top gear switch. If resistance is less than 5 ohms, repair open in IGNITION RUN circuit to SIL bulb socket. If resistance is 5 ohms or more, replace top gear switch.

17) Check Continuity Of SIL Circuit Turn ignition off. Remove SIL bulb. Disconnect 60-pin ECA connector. Inspect terminals, and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving ECA disconnected. Set DVOM on 200-ohm scale. Measure resistance between test pin No. 53 and SIL power contact at SIL bulb socket. If resistance is less than 5 ohms, replace ECA. If resistance is 5 ohms or more, repair open circuit.

18) Operation Of Thunderbird 3.8L SC SIL On 3.8L SC, SIL will come on and a chime will sound when ignition switch is in RUN position and engine is off. Depending on transmission type, SIL and chime will also activate under following conditions:

Greater than 93 MPH (4000 RPM) in third gear for A/T.
Greater than 121 MPH (4300 RPM) in fourth gear for M/T.

When this happens, ECA will take necessary action to prevent engine damage from overheating. If coolant gets too hot or vehicle remains at high speed for 60 seconds, ECA will shut off 3 injectors until a safe operating speed is reached or transmission is upshifted to higher gear. ECA action is independent of SIL and warning chime and will occur regardless of whether these circuits malfunction. If SIL is always on, go to step 23). If SIL is always off, go to step 19).

Fig 3: Shift Indicator Light (SIL) Circuits (3.8L SC)

19) Check SIL Circuit Fuse Turn ignition off. Remove and inspect SIL fuse. If fuse is okay, reconnect and go to step 20). If fuse is blown, repair short to ground between fuse and SIL bulb. Replace fuse, and check SIL operation.

20) Check SIL Bulb Turn ignition off. Remove and inspect SIL bulb. If bulb is okay, go to step 21). If bulb is burned out, replace bulb and check SIL operation.

21) Check For Voltage To SIL Socket Turn ignition off. Remove SIL bulb. Set DVOM on 20-volt scale. Turn ignition on. Measure voltage between power contact at SIL socket and chassis ground. If voltage is more than 10.5 volts, go to step 22). If voltage is 10.5 volts or less, repair open circuit in IGNITION START RUN circuit to SIL bulb socket.

22) Check Continuity Of SIL Circuit Turn ignition off. Disconnect 60-pin ECA connector. Inspect terminals, and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving ECA disconnected. Measure resistance between test pin No. 53 at breakout box and SIL power contact at SIL bulb socket. If resistance is less than 5 ohms, replace ECA. If resistance is 5 ohms or more, repair open circuit.

23) Check SIL Circuit For Short To Ground Turn ignition off. Disconnect 60-pin ECA connector. Inspect terminals, and repair if damaged. Turn ignition on. If SIL is on with ECA disconnected, repair short to ground between SIL bulb and ECA. If SIL is not on with ECA disconnected, replace ECA.