why are my dash light brighter during the day and dim at night or during inclement weather?

Try adjusting your dimmer switch to high with the head lights on?

tried this already. during recent storm they switched from bright to dim automatically then back to bright when storm was over. same when going through a tunnel.

Oh ok. Sounds like the dimmer control could be acting up. When your head lights are on you should be able to adjust the brightness of the dash lights either up or down using the dimmer switch. When head lights are off most systems have a default light setting for the dash lights/read outs on the dash. My truck is much brighter with head lights off because I have the dimmer setting much lower when head lights are in the on position. Might have to turn light switch to the on position to adjust the dimmer vs having it in an auto head light setting. But when it is adjusted as you like it will work the same in the auto setting.

Thank you will give it another try.

your main ground is corroded...frequently people do not notice the "blue spark" that happens whenever the starter motor is engaged...this "blue spark" is caused by dis-similar metals sharing capitol amperage...needs to be wirebrushed shiny both lug and chassis/ground....with a NEW battrey, you'll have no more trouble then~