Ignition problems on early 80's Ford inline 6

I'm working on an early 80's Ford sedan with an inline 6, and single barrel carb. The engine is turning over, but not firing. I'm not getting any spark
from the coil - due to the fact that the negative terminal has a constant ground. The positive terminal has 12 volts (as it should). It's a single pickup distributor. There's a detached ignition control unit mounted to the firewall. There are three wires leading from the ignition module to the distributor. It looks like one is ground while the other two go to the magnetic pickup. When I disconnect the distributor from the ignition module, the negative terminal of the coil is no longer grounded.
Does this indicate a bad magnetic pickup in the distributor? What test can I do to determnine if it's the distributor or the ignition control?
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Connect a voltmeter across the battery, if voltage drops below 10.5 volts while cranking, the ignition system shuts down.
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How exactly were you able to determine this?

This is the correct ground path for Dura spark II. The black wire, from the module to the dist. body.

Hit the module with a mallet or similar object. This simple operation can often get you 3-15 miles down the road before it craps again. Or, install a new unit ($20) I seriously doubt if it's the pick up in the distibutor. The firewall module is prone to failure and I always carry a spare in my cars along with some basic tools. Otherwise I like the system. Works great.
DC
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