My battery is in trunk also, and grounded to frame back there, and block is grounded to frame up front.
The voltage in run, at the coil+, should be stepped down by the Ballast to about 7.5 volts or a bit more. During cranking that same post should be getting about same as what the starter is getting, about same as what the battery is reading. 10.5v is plenty for most coils. The Ecu could be getting a similar 10.5v during cranking. Obviously nothing can get more than battery voltage, but all those components will work, down to about 9.5 volts..... in my experience. Occasionally even lower.
To test the pick-up coil, I hook up an analog voltmeter at the pigtail, set to A/C volts and the smallest scale you have, then with pick-up still in D ,I just spin the mainshaft and watch the needle swing back and forth, indicating it is pulsing. With pick-up on the bench, I just wave a screwdriver over the magnet and again look for the needle swing. No needle swing is bad. It doesn't matter if the screwdriver or whatever wand you are using gets stuck on the magnet, just keep your eye on the needle when they separate.
