Audio Unit Button Illumination Does Not Work

WARNING: This page is about a different car, the 2006 Acura MDX, 2005 Acura MDX, 2004 Acura MDX, and 2003 Acura MDX. However, it is still accessible from the selected car via links, so may be relevant.

Turn the ignition switch to ON (II).
Turn the combination light switch ON (PARKING position).
Check the illumination of the audio unit buttons.
Are the buttons illuminated?
1. YES - Intermittent problem: the audio unit is OK at this time. Check for loose or poor connections at audio unit connector A (20P).
2. NO - Go to step 4.
Check the illumination of several other buttons not related to the audio system.
Are the buttons illuminated?
1. YES - Go to step 5.
2. NO - Troubleshoot the interior lights. Start by checking the No. 10 (15 A) fuse in the passenger's under-dash fuse/relay box. If the fuse is OK, check for open in the wire between the passenger's under-dash fuse/relay box and the audio unit.
Turn the ignition switch OFF.
Disconnect audio unit connector A (20P).
Disconnect driver's under-dash fuse/relay box connector J (18P).
Check for continuity between audio unit connector A (20P) No. 19 terminal and driver's under-dash fuse/relay box connector J (18P) No. 6 terminal.

Fig 1: Checking Continuity Between Audio Unit Connector A (20P) Terminal 19 And Driver's Under-Dash Fuse/Relay Box Connector J (18P) Terminal 6
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?
1. YES - Go to step 9.
2. NO - Repair an open in the wire.
Turn the combination light switch ON.
Measure voltage between audio unit connector A (20P) No. 9 terminal and body ground.

Fig 2: Measuring Voltage Between Audio Unit Connector A (20P) Terminal 9 And Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there battery voltage?
1. YES - Check the connections at the audio unit connector A (20P). If all connections are OK, replace the audio unit.
2. NO - Repair an open in the wire.