Well, yes, let me explain a little better,
The grounds are very inportant as I said, battery ground to block, it should bolt directly to the block by the oil pressure sender. Another small wire from negative post on battery to the inner fender panel between battery and solenoid, a small wire from that same place going down to a cylindrical connector then into the wire harness. Another ground is bolted to the back of the head on the drivers side and to the firewall nearby with a small screw, this wire is usually a flat braided wire no covering if it's original. There is one on the passenger side below the egr valve area that comes from the injector harness and is bolted to the intake manifold or the back of the head, don't use the bolt that holds the air tube to the head, there are threaded bolt holes back there to use, its a little hard to find but it should be there. And the one by the computer in the passenger side kick panel, most grounds that screw to the body sheet metal are small sheetmetal screws with green heads.
Now about running the codes, disconnect the negative cable and turn the headlights on, this discharges any power left and alows a fresh start, turn lights off and hookup the battery cable.
Drive around to get the temps up to normal, some stop and go driving and also a steady 50 mph or more cruze so the computer experiences an array information so spend some time on the road, then run the codes, if the scanner does not work try the paper clip method, have pen and paper ready to write down the codes and report back.
If you can't run the codes with either methods you have a wiring or computer problem,