There is no "negative post of the distributor". If the starter is able to turn, the distributor grounds itself through the engine block. No external ground is needed, unless you've got one of those oddball distributors that reverses the polarity on the points every time the starter switch is pushed. Those systems got disabled almost as soon as they were introduced.
Check to be sure you don't have an unintentional ground where the wire from the coil attaches to the distributor. It's a common mistake to allow the stud that goes through the side of the distributor housing to get grounded. This prevents the points from opening and closing the circuit from the coil to ground. If you move the points from open to closed with a screwdriver with the ignition turned on, the coil should generate a high-voltage spark. If the primary circuit is grounded to the distributor housing, opening and closing the points manually won't make a difference.
Jerry
