1991 560sel has not ignition spark

my recently purchased used 560sel with 165k miles has been running fine except for a rough idle. i put in a new cap and rotor and the performance improved slightly.
Today the car will not start and has no ignition spark. Is there a way to determine if the ignition module is energized? Is there a relay that powers it up? What is the best way to determine what component has gone bad? The crank sensor? Ignition module? relays? etc etc etc. thanks richard H in Lake charles LA

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