"The specs say #1 terminal voltage should be 2.__ maybe for CIS not Jetronic? And I have 12.7v at #1 same as #15. Is this coaxial cable supposed to be some kind of voltage absorber/modifier?"
• Where are your "specs" coming from? Statically, I'd expect coil#1 to be the same as #15 (voltage from #15 reading thru the coil to #1). Coil #1 is controlled to time and produce the spark by "making and breaking" a ground path. (like the points in old style systems.)

What is the voltage at coil #15 while cranking? A loose/dirty connection might show 12.7 on a meter but fail to pass the needed current under load.

Assuming the coil #15 12V is good, it sounds like the problem could be in one these areas (tests follow):
1) Distributor Hall switch is not generating the timing pulse to the Igntion CU. (Or the pulse is not making it to the ICU.)
or
2) The Ignition CU is not using the Hall pulse to control Coil#1 ground.

"The grey wires also go to the Lambda O2 sensor and to the ECU"
• I think that's the (shielded?) wire from ICU #1 to ECU #1 to allow Fuel operation. (Dead Ignition means no fuel pumping.) I don't think the O2 sensor shares that circuit, but may have common coax shielding from signal wire connection on into the ECU.

"There is what I think is a test socket tucked up above the driver’s left knee with 5-7 wires into it, included are two grey “coaxials” with the jacket conductors rolled back and twisted together. Any testing that I can do here?"
• I've got no clue on this one. No test socket inside that I know of.
=================================>
The following tests assume a Bosch distributor. I don't know about the Chrysler white cap.

Three things are needed for Spark and then then Fuel:

A) To get sparks from the coil, the spinning distributor's "Hall Switch/sender" must send weak pulses (1 per cylinder/plug) to the Ignition Control Unit (ICU).

B) The ICU must then respond to each pulse by "triggering" the coil's negative terminal #1 to generate the high voltage that leaves the coil to be "distributed" to the proper plug.

C) At the same time, the ICU must also send timing pulse to the Fuel CU to energize the Fuel relay (or keep it energized), and control the injectors, etc.

Either test below can be done first, and both assume there is +12V at Coil terminal #15 with Key On.

Hall Switch Test (tests for A to initiate B and C above)
1) Pull coil wire, attach/adapt to spare (grounded) sparkplug.
2) Remove distributor cap.
3) Rotate engine till a Vane "window" is centered in front of the Hall Switch.
4) Turn Key ON.
5) Pass a feeler gauge blade (or similar) through the Hall Switch (simulating the moving Vane).
•) If the Hall Switch and ICU are OK, you should get a spark and fuel pumps should run for a second.
•) Repeat step 5 as needed to verify spark and pumps.
•) If no spark, test ICU operation below (eliminating Hall Switch).

ICU Switching Test (bypasses A and tests only for B and C)
1) Key OFF. (Coil wire and spare plug still set up as in Step 1 above).
2) Remove the ICU 3-wire plug from distributor body.
3) Insert a jumper from plug socket B (Yellow wire) to socket C (Black wire). When jumper is REMOVED (step #4) the plug should spark, and the fuel pumps should run briefly.
4) Key ON. Check for spark and pumps as jumper is removed.
•) If Spark & Pumps now, suspect Hall Switch or wiring.
•) If no spark, suspect ICU or wiring.



--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.