Dash lights on/off

Hi, don't know what is going on so thought I would check with the experts :) I have a 99' Cadillac STS and for some reason the dashlites will dim to nothing then come on as bright as ever it also does this at the same time to
my radio lights. Anyone have an idea what to check for? Also from time to time My drivers seat will not go all the way forward to the seat adjustment. I will have to turn the key off and put the key back in and start it and it will work just fine then
Appreciate any help what to look for

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