Oil Pressure problem

[brad`]

Hey recently... for some reason only at night.. my oil pressure guage will drop to zero and sound that stupid high pitched beep... but other times/days it wont do it. One of my mates said it might be a loose wire going to the sensor. 2 thinks wrong.. 1) no idea were the sensor is 2) never had to deal with sensors. I owned an 83 Mazda 626.. so im still new with all the electronics