Take the wire going to the distributor off at the neg side of the coil and repeat your test. You should read 12V on both sides of the coil. (If the points are in the closed position a good coil could possibly read what you are seeing)

Another way to test the coil is to remove the wire from the center of the distributor cap and hold it (with insulated pliers or gloves) about 1/4" away from a good ground. Turn the key on and manually open and close the points, you should see a good spark jumping to ground.