A dash ammeter is a good example of the "measure with a micrometer- - - -mark with chalk- - - -cut with an axe" principle. All ammeters have a "shunt" that bypasses the meter movement and only uses a tiny trickle of juice to move the needle. Doubling the voltage doesn't change the deflection of the needle much, if any. PM me for a work-around modification to prevent the needle from pegging out during heavy current operation right after startup.
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!