If the display function does not work, replace the meter unit.

Check 3-6: Neutral Indicator Light (LED) Inspection
Meter Unit Circuit (ZX1000J Model)Subthrottle Sensor Output Voltage Inspection
Measure the output voltage at the subthrottle sensor in
the same way as input voltage inspection, note the following.
Disconnect the subthrottle sensor connector and connect
the setting adapter [A] between these connectors.
Special Tool - Throttle Sensor Setting Adapter: 57001
-1538
...
Drive Chain Slack Inspection
NOTE
Check the slack with the motorcycle setting on its sidestand.
Clean the chain if it is dirty, and lubricate it if it appears
dry.
Check the wheel alignment (see Wheel Alignment Inspection).
Rotate the rear wheel to find the position where the chain
is tightest.
Measure the ver ...
Meter instruments
Upper Button
Lower Button
Tachometer (with Shift-Up
Indicator)
Red Zone
Ambient Brightness
Sensor
Turn Signal Indicator Light
Warning Indicator Light
(Red)
Neutral Indicator Light
Multifunction Meter
High Beam Indicator Light
Warning Indicator Light
(Yellow)
Fuel ...