1989 Mercedes Benz the oil pressure is up when the engine is cold when you put your feet on the gas it go back up but while you are waiting for the light to change it drop to near zero?

The chances are good that it is the oil pressure switch. As long as it goes up when you hit the gas, and as long as the engine isn't making any noise (excessive ticking or rapping) then you don't need to worry about it. Change the pressure switch only if it annoys you, oherwise, just get use to it. There is also an "idiot light" for the oil pressure, so if you really loose the pressure, that should come on. You can turn the ignition key to the on position to make sure it lights up.