electrical problem on 2000 Ford F-250 Super Duty

Why does everything die when I turn the key to start? Battery is fully charged.

Asked by for the 2000 Ford F-250 Super Duty
1 answer
If you turn on the ignition key and everything dies check the battery voltage with a volt meter it should be 12.6 volts at rest and as someone cranks the engine over check the battery voltage using a voltmeter with the leads connected directly at the positive and negative connection of the battery the voltage should not drop below 9.6 volts or so with a draw of 200 amps after 15 seconds or the battery is not sufficiently charged or the battery is bad. Check and see if the battery connections are clean tight and secure,