[jjk3]

If the ignition switch was bad it still wouldn't start with the charger on there. Take a voltmeter and make sure you have voltage to the starter solenoid while cranking. If you do, then you know the ignition switch is good. Also, put your voltmeter across the battery. While cranking it should not drop below 9.6V or so (I'm a little fuzzy on the exact number).

Take an ohmmeter and test the resistance between the negative battery terminal and the engine block. You should read 0.1 ohms. Generally anything up to 0.5 ohms is acceptable, but the lower the number the better. If you have excessive resistance in the ground circuit, then you just found your problem. My best guess is that you have a grounding issue. Make sure the connections are clean, tight, and free of any paint, etc. Good luck. John