Final answer:
If the P-lead is disconnected in an aircraft magneto system, the magneto remains hot, making the ignition system live and creating potential safety hazards.
Step-by-step explanation:
In the aircraft magneto system, if the P-lead is disconnected, the magneto will be hot.
The P-lead is a grounding wire that when connected, allows a pilot to control the magneto switch, turning it on or off. With the P-lead disconnected, the magneto is always live or in an 'on' state, creating a risk for unintended engine starts if the propeller is turned because the magneto can still ignite the engine cylinders. This is particularly important to remember during maintenance procedures to ensure safety. In simple terms, with a disconnected P-lead, the ignition system is in an uncontrolled state.