Oil pump pressure problem

First question: Does your drill run backwards (counter clockwise)? The standard rotation for drills is clockwise. The oil pump needs to turn counter clockwise to pump oil.

Question 2: Did you have the ignition switch in the Run position and have power to the dash gauges?

Question 3: did the dash voltmeter show 12 volts or more with the ignition switch in the Run position?

You may need to use a mechanical gauge with a T fitting at the place the stock gauge sender connects to the engine. That way you can monitor the oil pressure while you run the primer.