Odometer light is dim. Fuse is ok. What is the problem?

I've got a similar problem , dash goes dim , shift indicator and radio , touched the dimmer switch on the light switch all worked , was going to replace that switch for 50 bucks but, read that it could be the day night sensor or resistors in the dash cluster electrical panel , this is a much cheaper fix but more labor , my Buick has 145,000 miles so I'm just going to replace , day night sensor & either re-solder or replace those resistors , search for this on the net & you will find videos on this fix

My dash lights went dim and I tried everything to fix them, One day my wife washed my car and cleaned the dashboard with warm water and the next time I used the car the lights came back to full brightness. This made me very happy but then a week later back to dim again, I keep a pad for my cellphone on the dash and noticed it was covering the red light so I took it off the light and they are bright again. So keep the dashboard clean and make sure nothing is on the dash sensor. I hope this helps everyone, Jim

Where would I check the dash light at ..how to get to them