1990 Corolla 4 Door With 94k - Do I need new oil pump - Oil light comes on when hard braking - Mechanic should fix?

As far as I know, the oil pump and the brake system have nothing to do with each other. However, the brake system uses enging vacumn to assist braking. When you push down hard on the brake pedal, it causes the engine vacumn to diminish. This may result in the engine not getting enought fuel, because vacumn is involved in determining fuel mixture. If the oil light goes out within a second or two of releasing the brakes, I wouldn't worry about it. If it stays on for longer than that, it could mean that the engine needs to be serviced. If you have not had the spark plugs changed since the car was new, it is time to change them. Also, the air cleaner element probably needs to be changed.