if you can hear the arcing, my experience has been it is probably not the vehicle electrical (6 or 12v) but ignition. Sounds like you are on the right track with what you did on the dist cap etc. Another trick is to look under the hood at night (darker the better). The arcing you hear should show up at in the dark! (I have found some bad plug wires that way, or the coil wire as well!)
