Wire a good-sized light bulb, like one for a brake light, to the hot side of the coil. Other than maybe having to recharge the battery occasionally, there's no downside- - - -more light under the hood to work by, and you've got a very effective visual reminder that the switch has been left in the "on" position.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!