Gauge Control Module (Tach) Input Test
  1. Turn the ignition switch OFF.
  1. Disconnect the gauge control module (tach) 36P connector.
  1. Inspect the connector and socket terminals to be sure they are all making good contact.
    • If the terminals are bent, loose or corroded, repair them as necessary, and recheck the system.
    • If the terminals are OK, go to Step 5 .
  1. With the connector still disconnected, make these input tests at the connector.
    • If any test indicates a problem, find and correct the cause, then recheck the system.
    • If the input tests prove OK, go to Step 6 .
    Cavity
    Wire
    Test condition
    Test: Desired result
    Possible cause if result is not obtained
    15
    BLK
    Under all conditions
    Check for continuity to ground: There should be continuity.
    • Poor ground (G502)
    • An open in the wire
    16
    BLK
    Under all conditions
    Check for continuity to ground: There should be continuity.
    • Poor ground (G503)
    • An open in the wire
    18
    WHT
    Under all conditions
    Check for voltage toground: There should be battery voltage.
    • Blown No. 16 (15 A) fuse in the under-hood fuse/relay box
    • An open in the wire
    17
    LT BLU
    Ignition switch ON (II)
    Check for voltage toground: There should be battery voltage.
    • Blown No. 10 (7.5 A) fuse in the under-dash fuse/relay box
    • An open in the wire
    20
    LT GRN
    Under all conditions (disconnect the gauge control module (speedo) 12P connector)
    Check for continuity between the No. 20 terminal and the gauge control module (speedo) 12P connector No. 7 terminal: There should be continuity.
    An open in the wire
    Attach to ground: There should be no continuity.
    A short to ground in the wire
    13
    BLU
    Combination light switch ON
    Attach to ground: The dash lights (LED) come on.
    • Faulty dash lights (LED)
    • An open in the wire
    14
    PUR
    Combination light switch ON
    Attach to ground: The dash lights (bulbs) and audio unit light come on.
    • Faulty dash lights (bulbs)
    • Faulty audio unit light
    • An open in the wire

  1. Reconnect the connector to the gauge control module (tach), and make these input tests at the connector.
    Cavity
    Wire
    Test condition
    Test: Desired result
    Possible cause if result is not obtained
    24
    LT BLU
    Ignition switch ON (II), select/reset switch pressed
    Check for voltage to ground: There should be less than 1 V.
    • Poor ground (G503)
    • Faulty select/reset switch
    • Faulty cable reel
    • An open in the wire
    Ignition switch ON (II), select/reset switch released
    Check for voltage to ground: There should be 5 V or more.
    • Faulty select/reset switch
    • Faulty cable reel
    • A short to ground in the wire
    25
    GRN
    Ignition switch ON (II), information switch pressed
    Check for voltage to ground: There should be less than 1 V.
    • Poor ground (G503)
    • Faulty information switch
    • Faulty cable reel
    • An open in the wire
    Ignition switch ON (II), information switch released
    Check for voltage to ground: There should be 5 V or more.
    • Faulty information switch
    • Faulty cable reel
    • A short to ground in the wire
    27
    ORN
    Ignition switch ON (II), brake fluid is full level in the reservoir
    Check for voltage to ground: There should be less than 1 V.
    • Poor ground (G401)
    • Faulty brake fluid level switch
    • An open in the wire
    Ignition switch ON (II), brake fluid is lower level in the reservoir
    Check for voltage to ground: There should be 5 V or more.
    • Faulty brake fluid level switch
    • A short to ground in the wire
    28
    LT GRN
    Ignition switch ON (II), parking brake lever pulled
    Check for voltage to ground: There should be less than 1 V.
    • Faulty parking brake switch
    • An open in the wire
    Ignition switch ON (II), parking brake lever released
    Check for voltage to ground: There should be 5 V or more.
    • Faulty parking brake switch
    • A short to ground in the wire