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take the hot wire off the batt while it is running....if it shuts off the alt is bad




Don't do this, not only is it an unreliable test of an alternator, it can damage other components when the battery is removed from the system. The battery serves as a cushion to protect against spikes.



i disagree. its not the best test but it would work. and these cars are pretty stout when it comes to electronics susceptable to voltage spikes.

If youre really concerned, then dont reconnect the battery if the car stays running with the ignition on. have someone turn off the ignition before reconnecting it. then there will be no spike so no possible damage

but a voltmeter would be best. check battery voltage at the alt outpput with the car off and then with it running. voltage should be a few volts higher with the car running



!!! DO NOT EVER DO THIS !!!

I've actually checked this years ago with a "test pig" that had no electronic anything. Disconnecting a charging unit from the battery generates OVER A HUNDRED volts of spike. I don't have it anymore, but I once had a 'scope photo of this spike, and used to haul it out for guys like you

One modern cars, with electronics of all kinds, solid state controls, radios, regulators and ignition, this is a GUARANTEED way of frying something. Yep---I know you "got away with it"---you might get by over a hundred times, and the 103rd time you do it, "the guy" might say, "Ya know, it's funny, when YOU worked on my alternator 'thu udder day' the RADIO quit working."





Disconnecting the battery on any vehicle while the vehicle is running is nothing but stupid. Its just as you say, it generates a huge spike, thats capable of serious damage. Oh, it might not be immediate, but it damaged something!

Ya know, I argued back and forth with a few know-it-all hacks here a few years ago over this very topic. Some people just dont want to learn.

The good news is most people get away with it because their alternator is actually bad (disconnecting it also can damage it too) and there is no spike. However, if its working....its a different story.