Dash lights and climate control

My dash lights on my 92 Eldorado didn't come on at first but after the car is running they dim up to bright at first but now won't come on at all. At the same time the heater blower is not work either after the water pump and radiator was replaced I have heat but the climate controls fan does not engage as well. How do I go about diagnosing this problem? I read about a box near the gas pedal, that would fix both? Also it could be fuses, loose wire harnesses, or the heater blower as a possibility?