On my Valiant, I put a 1/8"NPT street tee in the engine block. One side of it feeds a mechanical underdash gauge, and the other side has an
Allstar ALL99059 oil-pressure switch in it for the dash light. Why the Allstar switch? It turns the light on at 20PSI rather than the OE switch's 4-7, which gives a greater safety margin. The light on the dash is nice and bright, even with a stock bulb. You immediately notice something that's not normally there.
I started using a dual setup in 1996 after a freak oil-pump failure. I'm good about watching my gauges, but a few seconds after checking 'em at a stoplight my 440 suddenly started making valvetrain noise. I looked back at the gauge and had virtually zero pressure. The retaining plug for the bypass valve had come out of the oil pump (a Melling). It was pinned against the motor mount by the spring, which was still in the almost-exposed valve on the other end. Thank God both sides of that spring are in a cupped orifice--I didn't lose any parts. I replaced the pump anyway, since one can do that on a 440 in half an hour in a Hardee's parking lot. The engine survived. I now religiously check every fastener on an oil pump before installing it, and have a dash light for those moments of inattention.