I do have some other issues in the instrument panel; the tach quits working sporadically, and often the ABS light comes on when the tach quits and goes out again when it kicks back in.

I will use a mechanical gauge to confirm the oil pressure, if it is OK will proceed with electrical checks.

If the oil pressure is truly fluctuating as shown on the gauge, what might be causing it? It seems to lose pressure inversely proportional to the load on the engine. Except in reverse, when the pressure jumps up to full when accelerating. It seems to come up when making a RIGHT turn also. Not so when turning left.