Panel 221VU uses LEDs for the backlight function. To drive the panel backlight you will need to supply 28 VDC and 5 VDC to the appropriate pinouts.

Thank you James for the assistance.

Pinouts

Outputs

(5 VDC)
671VC IR1 OFF 30/7 (gnd)
671VC IR1 FAULT 17/7 (gnd)
671VC ADR1 FAULT 22/7 (gnd)
671VC ADR1 OFF 21/7 (gnd)

673VC IR2 OFF 30/7 (gnd)
673VC IR2 FAULT 17/7 (gnd)
673VC ADR2 FAULT 22/7 (gnd)
673VC ADR2 OFF 21/7 (gnd)

675VC IR3 OFF 30/7 (gnd)
675VC IR3 FAULT 17/7 (gnd)
675VC ADR3 FAULT 22/7 (gnd)
675VC ADR3 OFF 21/7 (gnd)

671VC ON BAT 11/15 (gnd) (Requires 28 VDC)

Inputs

671VC IR1 31/4 (gnd)
671VC ADR1 9/4 (gnd)
671VC NAV 12/4 (gnd)
671VC ATT 13/4 (gnd)

673VC IR2 31/4 (gnd)
673VC ADR2 9/4 (gnd)
673VC NAV 12/4 (gnd)
673VC ATT 13/4 (gnd)

675VC IR3 31/4 (gnd)
675VC ADR3 9/4 (gnd)
675VC NAV 12/4 (gnd)
675VC ATT 13/4 (gnd)

Older style ADIRS panel (SIMon A320) pinouts:

ADIRS CDU Panel 41 VU