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Home › Mercury › 1988 › Tracer 2D Hatchback, Standard › Repair and Diagnosis › Engine Performance › System › MPFI System › Circuit Tests › Test FG - Electrical Load Unit (ELU)

Test FG - Electrical Load Unit (ELU)

  1. System Inspection: Perform a visual inspection of wiring and harness connectors. Ensure cooling fan motor, blower motor, lighting system, BAC valve, alternator condition, idle adjustment and general engine performance are not malfunctioning before proceeding with test. If a problem is found with wiring or harness connectors, repair or replace as necessary. If cooling fan is not operating properly, go to next step. If blower control is not functioning properly, go to step 4). If defroster is not functioning properly, go to step 6). If combination switch is not functioning properly, go to step 8).
  2. Coolant Fan Temperature Switch Operation: Disconnect cooling fan switch. Turn ignition on. Using a DVOM, measure voltage between fan switch Yellow/Green wire and ground without piercing wire. With coolant temperature more than 206°F (97°C), DVOM should read no voltage. With coolant temperature less than 206°F (97°C), DVOM should read 10 volts. If DVOM reads correctly, go to next step. If DVOM does not read correctly, diagnose heating and air conditioning system.
  3. Coolant Fan Switch Operation At ELU: With ignition on, measure voltage between ELU Yellow wire and ground. With coolant temperature more than 206°F (97°C), DVOM should read no voltage. With coolant temperature less than 206°F (97°C), DVOM should read 10 volts. If DVOM reads correctly, go to step 10). If DVOM does not read correctly, repair Yellow wire between ELU and cooling fan switch.
  4. Blower Control Switch Operation: With ignition on, measure voltage between blower switch Blue/Green wire and ground with blower switch connected. With blower switch in "OFF" position, DVOM should read 10 volts. With blower switch in "LO", "ML", "MH", or "HI" position, DVOM should read no voltage. If DVOM reads correctly, go to next step. If DVOM does not read correctly, diagnose heating and air conditioning system.
  5. Blower Control Switch Operation At ELU: With ignition on, measure voltage between ELU Blue/Green wire and ground. With blower switch in "OFF" position, DVOM should read 10 volts. With blower switch in "LO", "ML", "MH", or "HI" position, DVOM should read no voltage. If DVOM reads correctly, go to step 10). If DVOM does not read correctly, repair Blue/Green wire between blower control and ELU.
  6. Defroster Switch Operation: With ignition on, measure voltage between defroster switch Black/Yellow wire and ground with switch connected. With defroster switch on, DVOM should read 10 volts. With defroster switch off, DVOM should read no voltage. If DVOM reads correctly, go to next step. If DVOM does not read correctly, diagnose heating and air conditioning system.
  7. Defroster Switch Operation At ELU: With ignition on, measure voltage between ELU Black/Yellow wire and ground. With defroster switch on, DVOM should read 10 volts. With defroster switch off, DVOM should read no voltage. If DVOM reads correctly, go to step 10). If DVOM does not read correctly, repair Black/Yellow wire between ELU and defroster switch.
  8. Combination Switch Operation: With ignition on, measure voltage between combination switch White wire and ground with switch connected. With headlight switch on, DVOM should read 10 volts. With headlight switch off, DVOM should read no voltage. If DVOM reads correctly, go to next step. If DVOM does not read correctly, diagnose lighting system.
  9. Combination Switch Operation At ELU: With ignition on, measure voltage between ELU White wire and ground. With headlight switch on, DVOM should read 10 volts. With headlight switch off, DVOM should read no voltage. If DVOM reads correctly, go to next step. If DVOM does not read correctly, repair White wire between ELU and combination switch.
  10. ELU Operation At ECA: Disconnect ECA connector. Install breakout box. Turn ignition on. Using a DVOM, measure voltage between pins No. 24 and 40. Operate one switch at a time leaving all other switches off. See SWITCH VOLTAGE SPECIFICATIONS table. If DVOM reads correctly, replace ECA assembly. If DVOM does not read correctly, go to next step.
    SWITCH VOLTAGE SPECIFICATIONS

    Switch Position Approximate Voltage
    Blower Control "OFF" 10
    Blower Control "ON" 2.5
    Combination "OFF" 10
    Combination "ON" 2.5
    Cooling Fan "OFF" 10
    Cooling Fan "ON" 2.5
    Defroster "OFF" 10
    Defroster "ON" 2.5
  11. ELU Operation: With ignition on, measure voltage between ELU Black wire and ground. Operate one switch at a time leaving all other switches off. See SWITCH VOLTAGE SPECIFICATIONS  table. If DVOM reads correctly, repair Black wire between ELU and ECA. If DVOM does not read correctly, go to next step.
  12. Power At ELU: With ignition on, measure voltage between ELU Yellow/Green wire and ground. If DVOM reads more than 10 volts, go to step 14). If DVOM reads less than 10 volts, go to next step.
  13. Power At Power Relay: With ignition on, measure voltage between power relay Yellow/Green wire and ground with relay connected. If DVOM reads more than 10 volts, repair Yellow/Green wire between power relay and ELU. If DVOM reads less than 10 volts, go to TEST FC  .
  14. Ground At ELU: With ignition off, measure resistance between ELU Black wire and ground. If DVOM reads more than 5 ohms, replace ELU. If DVOM reads less than 5 ohms, repair Black wire between ELU and ground.
Fig 1: ELU Circuit
G94548
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