99 Mazda Millenia grounding problem?

[MazdaRICK]

I have a 99 Millenia S with 273,000 km. Im having problems with what i believe is a grounding problem. Sometimes the radio wont work but once i press the window button it starts to work. Others is when i turn on my headlight and it makes a popping noise in the speakers. Also, when i step on the brakes, the headlights and cluster guage light dim at the same time. Sometimes when i turn on the headlight you'll see the cluster guage shut off completly then come back on. The car also idles really low and sometimes feels like its cutting off. Please, if you can help me with any of these that would be great. Thanks