1980 Other GMC Models Start but No Run

Electrical problem
1980 Other GMC Models V8 Four Wheel Drive Automatic

I have a 1980 GMC K2500 that has all of a sudden developed some strange problems. I started it up and the alt gauge buired the needle past 18 volts. I then shut it off and now the truck will start and fire but not run. I assumed there was an electrical short and began to diagnose the problem. Upon trouble shooting I disconnected the starter wires and the alt wires from any contact with the rest of the positive system or ground. I began running tests with my DMM meter and found that in the run position, on the ignition switch. With the meter connected to the junction block and to ground there is a direct connection to ground. Is this correct in the wiring. If not, and I assume not. Is it possible that the ignition switch is the problem? I have checked all of the wiring under the hood to the fuse box and all is ok. How would I go about testing the ignition switch?

Thank you