I've watched voltage spikes of over 100V on an oscilloscope when somebody pulled a battery cable with the engine running. If you're doing it on a stone age vehicle without a lot of electronics you might get away with it, but even a built-in regulator on a 10SI alternator can be fried that way. Ditto for that sound system you just spent a couple of paychecks on. Computers really dislike voltage spikes.
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!