Also from the Navy site
"Aviation Machinist's Mate (AD): Usually, ADs are assigned to billets concerned with maintaining turbo-jet aircraft engines and associated equipment or to any one of several types of aircraft maintenance activities. ADs maintain, service, adjust and replace aircraft engines and accessories, as well as perform the duties of flight engineers. "
and
"Aviation Electrician's Mate (AE): AEs maintain, adjust and repair aircraft electrical power generating and converting systems; lighting, control and indicating systems; and can install and maintain wiring and flight and engine instrument systems. "
and
"Aviation Electronics Technician (AT): Modern aircraft depend on radio, radar and other electronic devices for rapid communications, effective navigation, controlled landing approaches and neutralizing enemy equipment and tactics. ATs are responsible for the test, maintenance and repair of this equipment. "
I can't say that there aren't electronics associated with aircraft engines, but we tend to separate them for work load purposes. ADs work on aircraft engines. AEs and ATs work on aircraft electrical stuff.