Greetings and Happy New Year from Colorado.

I'm hoping someone will have an answer to a question. The illumination lights behind the buttons on my stock radio (2001 Tundra) are very dim. All other lights on the dash and even the radio LCD screen work properly and vary from bright to dim with the rheostat. But the button lights go from very dim to off with the rheostat. It's a pain when night driving to try to find the right button. I pulled the radio apart and each button has a tiny LED behind it. They work, just very dimly. I think LEDs are dimmed using PWM (pulse width modulation) but I can't find where the pulsed signal would come from to even test.

Does anyone have suggestions on a possible cause and how to troubleshoot?

Thanks!