John P:
Here is a simplified Schematic of the Ignition Switch.
Remove the wires from the Switch. Set a VOM set on the Resistance Scale. There should be NO continuity from B to I nor N to S.
Turn the switch to the "on" position. There should be continuity (Zero Ohms) between B & I.
With the switch in the "start" position, there should be continuity (Zero Ohms) between B & I and B & S.
If you don't have any of the above, then the switch is bad.
Bear in mind, that this test is under a "no load" condition. It is usually accurate. However, it is possible, with the wires attached to the switch and under a typical load, the results may differ.
You could perform a Voltage Check with the Wires attached as follows.
With the VOM set at DC Voltage Scale, and the Black Meter lead attached to the Battery ( - ) terminal or a good chassis ground, you should have the following, considering the battery is in good condition and fully charged:
With the Red Meter Lead, you should have:
~12VDC at the B terminal
With the Igntion Switch in the On position, you should have ~12VDC on the "I" terminal.
With the Ignition in the Start Position, you should have ~12VDC on both the I & S terminal.
Hope this helps....