What can cause a coil to fail in a Distributorless Ignition System (DIS)?

In a Distributorless Ignition System (DIS), a damaged ignition wire can indeed lead to coil failure. The ignition wires are responsible for transmitting the high voltage generated by the coil to the spark plugs. If an ignition wire is damaged, it can lead to increased resistance or a short circuit. This resistance can cause the coil to overheat as it struggles to deliver the necessary voltage to the spark plugs, which can eventually lead to coil failure.

The other options, while they may cause issues in the ignition system, do not directly lead to coil failure. A faulty starter motor primarily affects the starting of the engine, and low battery voltage would mainly cause poor performance or starting issues rather than directly damaging the coil. Similarly, a defective spark plug can lead to misfiring but would not typically cause a coil to fail; rather, it might cause the coil to work harder than normal while trying to compensate for the poor spark plug performance.