No spark at plugs on my 1991 volvo 240

Best to ask a Volvo forum
Volvo 850 plug wires order Volvo Performance Repairs And Modifications

The speed sensor or crank sensor as called by other vehicles is on the rear pass side. Follow a black wire that looks like a spark plug wire. It has a connector and 1 bolt where it attaches near trans. Well known for failing and no spark.

this video could be a possible solution to your problem or your vehicle may have an igniter assembly or coil that needs replaced

SOUND LIKE BAD DISTRIBUTOR CAP AND ROTOR,SPARK PLUG WIRE ALSO COULD BE BAD.

CHANGE OUT THE COIL!

On older types 240 there was some kind of antitheft system connected with the steering lock. Try to route a lead from the battery to the ignition coil and se if it starts.
I drove a 240 with a separate ignition switch all through high school.

I believe this a belt driven engine right? Check the timing belt.

Google Volvo wiring diagram. They are available free. The diagram shows the wire location and colors. Otherwise, run a continuity test with a simple meter to discover a connection with some resistance between a pair of wires. If you here a click or two, from the speakers, you have found the right pair. Continue and label the pairs left, right, front,rear, until all are identified. Then reconnect. A pain but not rocket science.

If you are sure about spark----there is an inline fuse on left front fender in engine compartment.If this is not it then get the Bently manual from IPDUSA.COM

Try a new engine rpm speed sensor. It is located at the back-top of engine block where it mates to trans. You will need to remove a single bolt (10mm socket or wrench). You may have to wiggle the sensor to lift it out. Another symtom you may experience, is when you are cranking the car to start, it will buck and act like it is out of time. Another possible component is the ignition power stage/amplifier.