LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Ford >> 1989 >> Thunderbird Base >> Repair and Diagnosis >> Engine Performance >> System >> 3.8L CEC Tests W/Codes >> Circuit Tests >> Circuit Test B14
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Circuit Test B14

NOTE: Perform this test when Service Code 74 or 75 is displayed during QUICK TESTS or when directed here by other test procedures.
Fig 1: Brake ON/OFF (BOO) Circuit (3.8L SEFI AXOD)
G112596
Fig 2: Brake ON/OFF (BOO) Circuit (3.8L SEFI RWD, 3.8L SEFI SC)
G112598
Fig 3: Brake ON/OFF (BOO) Circuit (3.8L SEFI AXOD)
G108572

To prevent replacement of good components, be aware that the following non-EEC related areas may be at fault: brake light bulb, brake light switch, or brake light fuse. This test is intended to diagnose a faulty BOO circuit or ECA.

  1. Code 74: Verify Brake Pedal Was Depressed. If brake was NOT depressed during KOER SELF-TEST, repeat test and depress brake pedal ONLY once during test. Depress and release brake pedal AFTER dynamic response code but before brief WOT. If pedal was depressed, go to next step.
  2. Checking Power Circuit. Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion, and loose wires. Install breakout box, leaving ECA disconnected. Set DVOM on 20-volt scale. Measure voltage between test pins No. 2 and 40 while applying and releasing brake. If voltage cycles, switch circuit is okay, replace ECA and repeat QUICK TEST. If voltage does not cycle, go to next step.
  3. Checking For Shorts To Ground. Turn key off. Leave breakout box installed and ECA disconnected. Set DVOM on 200K-ohm scale. Disconnect BOO circuit at 12-pin connector (14290 Harness). Measure resistance between test pins No. 2 and 40 at the breakout box. If resistance is greater than 10K ohms, repair stoplamp circuit as necessary. If resistance is less than 10K ohms remove breakout box repair short, and repeat KOER SELF-TEST.
  4. Code 75 Displayed. Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect for and repair any damaged wiring. Install breakout box, leaving ECA disconnected. Set DVOM on 200-ohm scale. Disconnect BOO from Transmission Hydraulic Switch 12 pin connector (14290 Harness). Measure resistance between test pin No. 2 and BOO circuit at the 12-pin connector (14290 Harness). If resistance is greater than 5 ohms, remove breakout box. Reconnect ECA, repair open circuit, and rerun SELF-TEST.
  5. Code 75: Cycle BOO Circuit. Turn key off. With breakout box installed and ECA disconnected, set DVOM on 20-volt scale. Measure voltage between test pins No. 2 and 40 at the breakout box while depressing and releasing the brake pedal. If voltage cycles, remove breakout box. Replace ECA, and rerun QUICK TEST. If voltage does not cycle, go to next step.
  6. Checking BOO Circuit For Short To Power. Turn key off. Install breakout box, leaving ECA disconnected. Set DVOM on 20-volt scale. Disconnect BOO circuit at 12-pin connector. Measure voltage between test pin No. 2 at the breakout box and engine block ground. If voltage is greater than 10.5 volts, BOO circuit is okay. Check and repair brake light circuit as necessary. If voltage is less than 10.5 volts, remove breakout box. Reconnect ECA, repair circuit short and rerun QUICK TEST.
  7. Code 74: Verify Brake Pedal Was Depressed. Code 74 indicates that brake was NOT depressed during KOER SELF-TEST, the BOO signal did not cycle during test. Repeat test and depress brake pedal ONLY once during test. Depress and release brake pedal AFTER dynamic response code, but before brief WOT. If pedal was depressed, go to next step. If voltage did not cycle, repeat KOER SELF-TEST and depress brake pedal once during test.
  8. Checking BOO Circuit Cycling. Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion, and loose wires. Install breakout box, leaving ECA disconnected. Set DVOM on 20-volt scale. Measure voltage between test pins No. 2 (pin No. 5 on 3.8L SEFI) and 40 while applying and releasing brake. If voltage cycles, switch circuit is okay, replace ECA and repeat QUICK TEST. If voltage does not cycle, go to next step.
  9. Checking Continuity of BOO Circuit. Turn key off. Leave breakout box installed and ECA disconnected. Set DVOM on 200-ohm scale. Disconnect BOO circuit at 12-pin connector (12A581 to 14290 or 14401 Harness Connector). Measure resistance between test pins No. 2 (pin No. 5 on 3.8L SEFI) and 40 at the breakout box. If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms remove breakout box repair open circuit, and repeat KOER SELF-TEST.
  10. Checking BOO Circuit For Short to Power. Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect for and repair any damaged wiring. Install breakout box, leaving ECA disconnected. Set DVOM on 20-volt scale. Disconnect BOO from Transmission Hydraulic Switch 12-pin connector (12A581 to 14290 or 14401 Harness). Measure voltage between test pin No. 2 (pin No. 5 on 3.8L SEFI) at the breakout box and engine block ground. If voltage is greater than 1.0 volt, remove breakout box. Reconnect ECA, repair short circuit, and rerun SELF-TEST. If voltage is less than 1.0 volt, go to next step.
  11. Check BOO Circuit For Short to Ground. Turn key off. Leave breakout box installed and ECA disconnected. Set DVOM on 200K ohm scale. Disconnect BOO circuit at 12-pin connector (12A581 to 14290 or 14401 Harness Connector). Measure resistance between test pin No. 2 (pin No. 5 on 3.8L SEFI) and test pin No. 40 at the breakout box. If resistance is greater than 10K ohms, repair stoplamp circuit as necessary. If resistance is less than 10K ohms remove breakout box repair short, and repeat KOER SELF-TEST.
scientia non olet · About LEMON Manuals