Troubleshooting Headlight, Brakelight, Taillight issues and other CMS Troubles

Problem: HEADLIGHT DOES NOT COME ON. (MONITOR DOES NOT LIGHT.)

Light lead connections:

HI: Yellow to Yellow/Green (or Yellow/Red)

Lo: Green to Green/Red

NOTE: On the XJ750, no lights will come on before the engine starts.

Disconnect the 3-P coupler (for headlight) in the headlight body, and check voltage.  Hi: Yellow/Green to Ground (B lead)  Lo: Green/Red to Ground (B lead)  *Main switch is ON	12V ►	Headlight bulb is burnt out.
Less than 12V ▼
Measure input voltage on the wire harness side through the 6-P coupler in the headlight body. Hi: Yellow to Ground Lo: Green to Ground •	Reads 12V ►	• CMS is faulty
Less than 12V ▼
•   Dimmer switch •   Starter switch •   Main switch •   Fuse Check the condition of these parts according to the electrical section of the service manual.

Problem: HEADLIGHT COMES ON AND MONITOR WILL NOT GO OFF.

•   CMS is faulty. 
•   LCD is faulty.
•   Connector is faulty.

NOTE: If the monitor (HEAD) comes on with the main switch turned on, both LCD and connector are in good condition. Replace CMS.

Problem: THE HEADLIGHT BULB IS NOT BURNT OUT, BUT THE MONITOR COMES ON.

•   Yellow/Green lead is broken. 
•   Green/Red lead is broken.
•   Black lead is broken.
•   Connector is loose.

TAIL/BRAKE LIGHT DOES NOT COME ON. (MONITOR DOES NOT COME ON.)

Light lead connections: 
Tail: Blue-Blue/White 
Brake: Green/Yellow- Yellow/White (or Yellow/Black)

Disconnect the 3-P coupler of the taillight, and measure voltage.  *Main switch is ON.  Tail: Blue/White to Ground (Black lead)  Brake: Yellow/White to Ground (Black lead) NOTE: Measure voltage when brake is applied.	12V ►	•   Burnt taillight bulb •   Broken lead •   Loose connections
Less than 12V ▼
Disconnect the Y/W and L/W leads from the monitor side of the 6-P and 9-P couplers, and check voltage.  Tail: Blue/White to Ground  Brake: Yellow/White to Ground Yellow/ Black NOTE: Measure voltage when brake is applied.	12V ►	•   Broken Yellow/White lead •   Broken Blue/White lead
Less than 12V ▼
Measure voltage of the L lead and G/Y lead on the wire harness side.  Tail: Blue lead from Main switch  Brake: Green/Yellow lead from brake switches	12V ►	•   CMS is faulty.
Less than 12V  ▼
•   Brake: Check the brake switch and leads. •   Tail: Check main switch and leads.

EXAMPLES OF OTHER TROUBLES

The computerized monitor system may malfunction under the following conditions, though it is in good condition. The term "malfunction" means an erratic change in the display when the computerized monitor is not operated.

1.    The battery is in a state of extremely low voltage. The computerized monitor system is so designed that it operates normally when a specific voltage is input. Therefore, if the battery has almost run down or sulfation, the system may malfunction.

2.    The computerized monitor system is interfered by radio noise. The system has a protective device against radio noise, but some special radio noise may cause the system to malfunction.

Radio noise can be produced in the following cases:
a.  When spark plugs without resistor are used on an engine for which spark plugs with built-in resistor should be used.
b.  When a special horn is used.

EXAMPLES OF ERRATIC LC. DISPLAYS

If any one of the following symptoms appears, the L.C. display is considered to be faulty.

1. Part of the L.C. display is chipped off.

2. The deflecting plate has scratches or cavities.

3.    Glass is cracked or chipped,

4.    Contrast is uneven on the same display.