The general consensus is not to have the car running. Reasoning seems to be the difference between the charging systems of a car and of a bike. I personally don't want to put my 20 year old motorcycle wiring system to the test. You are also assuming that the running car is working properly. Just food for thought in the end.

 

Yeah Kong, I think it is old wives tale. Bikes are always behind in technology, so I assume at one point many years ago, cars switched to 12V while bikes may have still been 6V. That or people jumping old car to new car got themselves in trouble jumping 6v with new 12v. Just a guess...

12 V is 12 V, old bike/old wiring doesn't matter as long as it is a 12v system. Now if the cars regulator was busted and you tried to jump off a running car, the alternator would push out way too much voltage and then cause a problem. But this problem would also screw up your car as well so yeah I am assuming the car works, but unless you are one unlucky SoB and your cars regulator stops working right just that second, then it shouldn't matter.

Dunno, I guess a voltmeter is always a nice thing. If your car is running and you see 14V, you are always in the clear so jump away, running or not. If you are completely unsure and don't have a voltmeter then sure, jump it with the car off.

Either way, we learned that it is the voltage that matters not amps. A car battery will most likely be putting 200+ amps into your bike to start it, and it is not a problem at all.