everything dims
 

when ever i turn my headlights on my oil pressure gauges goes up a little then if i turn fan on everything dims and if i turn fan wide open it dims down and the oil pressure goes up even higher and the volt meter drops. i have a brand new alternator in it and both batterys check good. When the head lights are on if i roll my window up the lights dim till i release button and when i hit my brakes they dim also does anyone might know whats going on??:argh: