Originally Posted by wstar

The accuracy of the volts or ohms reading might be affected, but any change in the "speed" of the signal is so small as to be completely ignorable. I doubt you could even find the equipment to measure it accurately



Well, the other side of that argument is that if you added the ground wires to a new car, they're going wear/corrode at the same rate as the factory wiring. At some point you'll have to fix one or both down the road.