Indeed, my boat has a Yanmar diesel engine from the 1980s. Except for the electrical needs of the starter motor, alternator, and a couple of alarm sensors, Yanmar and other makers of this vintage purposely made these engines to run entirely mechanically.
There are no digital controllers and no consequent promises of higher efficiency or reliability. More than one sailor I've talked to see this absence of electronics as a feature. Sailors are wary of gear that's difficult to understand.
With just a half-decent socket wrench set and a few other common tools, my delicate desk-job hands handle all maintenance tasks and most repairs.