cavalier dim odometer

After Best Buy installed Amp and subs to my factory RDS head unit on my 2000 Cavalier Z24, The digital odometer is almost un-readable. It still works but is very very dim.Of course they say that there is no way that they could have damaged it. What can I reference to show them otherwise.I have read that the radio, dash cluster,BCM and PCM are all connected. The chevy dealer quoted a price of about $350.00 to repair the dash cluster. Any input will be helpful.  p.s. Best Buy  installed a converter to get the RCA output to the amp and subs.

What wiring did they tap into for adding the extra audio equipment? Specifically, what did they use to trigger the amp and did they run the main battery line to the battery? There isn't a wire in the radio's plug to act as a remote turn on, so if they used a wire at the radio's harness, try disconnecting it and hook it to the 12 gauge brown wire off the ignition switch.sparky

Silly Q, But are you sure they havent simply turned down the dash lights, via the dimmer pot / dial? Regards EVIL Teken . . .