[MOTORHEAD]

The voltage drops only when current flows, so your module is turned "on". disconnect the connector at the dist. The voltage then should be approx 12 v on both ends of the ballast resistor. You did the test of the module as described in the link provided by Rick, voltage had dropped to approx 2v and did not recover as discribed in the test procedure, so the switching xstr is probably shorted, conducting all the time, which is why the voltage out of the ballast is low.
Module is bad. How long has this system worked for you before it failed ? Did it fail after the alternator rebuild ?