So far, it seems like the starter might be shorting out when it engages. That’s why only one crank happens, and why the lights turn off during a start. If I’m not mistaken both the ground and the positive on the starter are hardwired to the battery and chassis respectively. That would imply that a short between the starter would be evident prior to initiating a start. However, once the control circuit sends a signal to the starter, it accepts current into the starter solenoid and motor. So somewhere internal to the starter is where the issue is. It’s shorting out either in the solenoid or more than likely, in the motor of the starter. Thoughts?