hi mike,

i'm late to this thread due to a field trip to the hospital for a new
titanium rotor cuff.

my best hunch: you may have a bad ignition switch since it powers the main fuel relay via fuse 1

to test the fuel circuit, go get this handy gizmo at harbor freight.
you should see some value around 10+- amps with the engine running,
to insure the fuel wiring is well. sorry i dont have the 850 benchmark.

if fuse 1 one current flow is zero when your car when your car wont start,
it tells you to look at the fuel circuit. checking the main fuel relay, ignition switch and rsr.

https://www.brickboard.com/RWD/volvo/1685010/940/960/980/V90/S90/review_harbor_freight_30a_fuse_circuit_tester_67724.html

pay attention to the ten second time limit for current readings.

another possible culprit is the rsr , but check f1 first.

good luck, bill