I just went out and tested everything I could by myself. It's kind of rough getting good contact and turning over the motor at same time, with one person. So I didn't get all the possibilities.
Key on, two pin connector *disconnected* (small yellow wire) 5 volts DC to battery ground. Three pin connector large yellow wire, 13 (12) volts, to the battery ground.
*Coil disconnected* (removed), key on 13 (12) volts at the (firewall side) coil contact on the ignition control module. With all connectors connected.
No voltage reading on the two pin connector (small yellow wire), *with it connected* to the ignition control module and back pinned. I checked both the AC and DC voltage on a digital meter. If there was any voltage there, it was so low to be irrelevant. I guess the module dumps the 5 volt signal to ground, when the two pin connector is connected and the key is in the run position.
With the two pin connector (small yellow wire) connected to the ICM and *back pinned*, motor start (motor turning over), a digital multi meter got twitchy on the voltage numbers DC (10 volt scale) and the voltage numbers really got twitchy in the AC (10 volt scale). The same test with a analog (needle type meter), I tested using both the 2.5 volt scale and the 10 volt scale AC and DC. The needle would twitch once good, then just slightly shake. This is with the coil disconnected. I got better needle movement, with the meter on the AC scale.
I tested a stock XJ *coil*, it was 7 ohms between the two power leads and 4,700 ohms from the plus lead to the high voltage lead and 7,500 ohms form the negative coil lead to the high voltage lead. A coil with lower ohm readings may cause the ICM to overheat and/or fail.
I also tested the coil ground contact in the ICM (everything disconnected and no power), to the ICM ground pin and got 9,200 ohms. And 31,000 ohms between the two coil leads on the ICM, everything disconnected. I tried to read a 12 volt DC pulse, between the two coil connectors, with the motor truning over (connectors connected), with iffy results.