Ditto to Walrus3, it's a wiring thing.

My experience is with 240's, but there are a lot of similarities.

The oil pressure sensor is a pressure switch, closed until the pressure gets up to a pre-set level. I think its around 5psi.

When the pressure is below that level, the switch closes to ground and that lights up the dash indicator.

SO if the wire between the sensor and the dash light gets to ground anywhere, the light will come on. The flickering can indicate a bad insulation place that occasionally rubs a ground place.

Someone here will know what the routing of that wire is on your 740. If it is like a 240, there are a number of places where the wire can ground if the insulation is bad. It is one of the joys of using a handsome older vehicle. Things can happen that a new mechanic cannot imagine.

Good Luck,

Bob

:>)