Never disconnect a battery cable, engine running to "test"
 

Warning:
Never disconnect a battery cable while the engine is running to "test" the alternator.
Doing so causes high voltage spikes that damage the alternator as well as other electronics.

http://www.google.com/search?q=Never+disconnect+a+battery+cable+while+the+engine+is+running&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a
#
#
http://www.pacificpowerbatteries.com/aboutbatts/car%20battery%20faq/carfaq14.html



.

I thought it was okay to do this on older cars. Is the consensus that this is even inappropriate for vehicles that don't have significant electronics?

Answer
 

The odds of blowing the voltage regulator or diode bridge are high, even on a factory fresh unit.

Depending upon build quality, age, mileage, climate, road sludge, and several other factors.

The odds can reach 99% of blowing the voltage regulator or diode bridge.


.

Thanks Roy. You learn something new everyday at the Peach.