the points act as a low amp/ow volt on-off switch: applying the test voltage through them from the 6V battery and manually cycling them at low speed may not show a fault but when they are cycling quickly with the kick back voltage of the ignition (condensor protection) you may get an arc that does not show the coil a ground. especially with old points. your option would be to file them with a fine points file and possible drill out the center of the contact to reduce the chance of growing another 'tit' on the point surface. also look for stray ground paths from the distributor to the coil - lead.
