Abstract: An electrical starting system for a Diesel engine has a manual selector switch which is moved momentarily to a preheating position to energize a relay which is then held energized by a relay switch from a battery D.C. source until the engine combustion chambers have been preheated sufficiently by preheating plugs to enable starting to be effected, indicated by the switching off of an indicator lamp. Starting can then be effected by the selector switch. If the preheating of the engine is incomplete the indicator lamp remains lit. A thermometric cut-out switch inhibits the preheating relay when the engine reaches a threshold temperature, avoiding wasteful operation of the preheating plugs with a hot engine.