no tach jump so I started in on the ignition system.
I would start with the simple stuff first—the Coil Primary terminals. Take them on and off a few times to break thru any oxidation. IMO, cold weather increases the resistance at marginal connections. A bad Neg terminal will kill the tach AND the Ignition.
To be certain, I'd check for NO SPARK at a removed & grounded plug (rather than bet it all on the tach).

is there a way to trouble shoot the impulse sender?
Yes, but before I copy it from my Bentley, check the FAQ for Volvo Chrysler ignition trouble-shooting.(Your ICU does say "Chrysler" on top, right?)

1) Ballast resistor, where would this be if there is one? None on Chrysler Ignition
2) What should I expect to see for coil resistance? 1.0 to 1.3 Primary— 9,600 to 11,600 Secondary
3) The (grey) wire from the ICU to the Coil and thence to the FI brain is shielded...Where should ths be grounded?
Can't say. The Bentley shows it going to LH ECU pin #5 (as does the shield from the O2 sensor). But the ECU pin test says there should be NO continuity from pin #5 to ground. Which seems strange to me—not to ground the shielding.

OK so this just got stranger.. The parts shop says I have the wrong distro.. the one in the car is a 0 237 520 004 and has the integrated (square) connector,
How many pins? 2? or 3? My parts book says the 004 Dist. is for '85 and up.

My book shows one with a pig-tail connector What book, and explain pigtail connector...

That's all I have for now,

Bruce

PS, that starter socket is probably tucked behind one of the cable bundles on the left side of the upper firewall.
--
Bruce Young,
'93 940-NA (current)
'80 GLE V8 (Sold 5/03)
'83 Turbo 245
'76 244 (lasted only 255,000 miles)
73 142 (98K)
'71 144 (track modified--crusher bound)
New 144 from '67 to '78
Used '62 122 from '63 to '67