Cluster Woes

Oil pressure light only turns on when the pressure switch closes (completes circuit to earth)

Turn signals.
Turn signals get power through the flasher unit. The flasher only gets power when the key is in RUN and/or accessory position.
There is also a second path to the same lamps, this is through the hazzard switch. Exactly how this is done varied from year to year but in all cases the hazzard flasher is always connected to power (works with key off). I beleive in most years it has a fuse.