Instrument And Nav Screen Dim

[Bgcarl]

My '04 LS Ultra has dim instrument and NAV screen lighting. Noticed after dead battery and several attempted starts with clattering start solenoid. Did I upset the ECU with spikes? Installed new battery and initiated all resets as required. The previous feature of dimming when going in a tunnel or underpass no longer works and the display seems to always be in the "dimmed" mode. Also, the dimmer control on the dash seems to have only minor effect from full CCW to full CW. I set the brightness and contrast controls to maximum in the screen display setup. The automatic light control works as the headlights come on when it gets sufficiently dark so I believe the sensor on top of the dash is not the problem. The dealer wants to change the ECU for around $1400. I'm hoping there is a much easier solution.

I have the full set of shop manuals from Lexus specifically for the '04 LS but no useful clues. Any help will be very much appreciated.

Bryan