Awesome advice from everyone thanks.
That's essentially what I just came across online -
https://www.justanswer.com/volvo/1b9as-1991-volvo-740-oil-pressure-light-on-restart-knocking.html
The guy said his problem was a broken timing belt and had nothing to do with the oil, but otherwise the mechanics response sounds tailored to my set of particular problems with the oil. My car has shut off several times while driving it, but then turns right back over if I turn it completely off then on again. Sounds like my sensor is going wonky.
This sounds like my problem again except I've had no maintenance done to my head gasket or camshaft oil seals that I'm aware of -
https://www.matthewsvolvosite.com/forums/viewtopic.php?t=42014
This part sounded most interesting -
"There is a relief valve spring in the oil pump. If this is sticking the same symptom can occur. "
This also might explain my errant oil sensor light, although it's much more full on flickering now then faintly appearing for a while and going away. Still goes away for a bit though then comes back.
Would also explain that why my car auto shuts off while driving.
Found some interesting links pertaining to the oil pump removal/replacement, though they could be better -
http://www.volvotips.com/index.php/740-760-780/volvo-740-760-780-service-and-repair-manual/
http://www.volvotips.com/service-manual/volvo-740/Volvo-740-760-780-940-960-B204-B234-16valve-engine-service-manual.html
Page 60 describes how to take out and replace the oil pump. Hopefully it's just the sensor that I'm having problems with though.
So my first step is to check the wiring and sender, see if its loose or something. Replace the sender.
Second is
to test the oil pressure!
Looking for diagrams online to find where the oil sender/sensor unit is... Can anyone direct?