It sounds like you have a short where the wire from the coil to the distributor goes through the distributor housing.
Try this- - - -remove the distributor cap and tap the starter until the points are open, or put a piece of a business card between the points. With the ignition switch in the "on" position, remove the wire at the coil (-) terminal, the one that goes to the distributor. If you get a spark when you touch the wire to the coil terminal, you've got a short at the distributor housing.
Another test: touch an ice pick style test light to the distributor side terminal with its test lead connected to ground. When the engine is cranked over with the ignition on and the points adjusted properly, the light should flash on and off.
Jerry
