Location of crank sensor on 1991 volvo 940 se and do i need to get part from volvo dealership or would Lordco have it ?

how wold fix it on 740 mold

You will have to call the dealer and get the code (you will need the VIN or the radio model # and serial #). Since your radio display says off, you will have to leave the radio on with ignition key in the number 1 position until it says code. Then you can put in the code. Hope this helps.

there should be a schematic/label stuck inside the cover or molded into the cover to tell what is what.

Your public library will have a manual covering your mechanical repair. Moreover, they have the automotive shops online software called AllData. It is the best auto technician database available today. You can print out specific troubleshooting procedures, diagrams, step-by-step istructions, and soforth. The typical person cannot afford to pay for this service, just automotive dealerships, etc... that is why the public library made it available to everyone and for free to view and print out material. This should Fixya! Good Luck!

take off cover to fuses in the centre consol reachin and push down the large black relay i get this myself on my volvo 940 1991 this relay does a number of things but to long to explain

Had you had the car scanned? It could be something else? Fuel pump, relay, fuse...
Is there any spark at the plugs? Is there fuel coming to the injectors?
There are a few things that can cause a car not to start, Is the engine light on?
Best way is to get the car scannd, if not you'll end up replacing unneccesary parts by trial and error.
Cheers

Sounds like you need an O2 sensor. You need to have it scanned, places like AutoZone will do this free of charge.

no, its on the bottom, big 1" brass plug very bottom of engine, easiest to get to from the front, I own the same car....

on the engine drivers side below the air intake/below the brake fluid reservoir/ follow the large red batery cable