Mark & Andrew,
I do not have a ballast resistor in the system. I run a MSD6AL and Blaster 2 coil-these have been on the car for years. When I checked the sense line voltage at the VR, I removed the VR plug, positive side of the meter directly into the plug female connector and negative side of the meter to the VR bolt that also holds the ground strap to the engine. The VR plug connects quite tightly to the VR terminals-it requires some effort to remove the plug.